From: Jacob Pan <[email protected]>
Freezer subsystem is used to manage batch jobs which can start
stop at the same time. However, sometime it is desirable to let
the kernel manage the freezer state automatically with a given
duty ratio.
For example, if we want to reduce the time that backgroup apps
are allowed to run we can put them into a freezer subsystem and
set the kernel to turn them THAWED/FROZEN at given duty ratio.
This patch introduces two file nodes under cgroup
freezer.duty_ratio_pct and freezer.period_sec
Usage example: set period to be 5 seconds and frozen duty ratio 90%
[root@localhost aoa]# echo 90 > freezer.duty_ratio_pct
[root@localhost aoa]# echo 5000 > freezer.period_ms
Signed-off-by: Jacob Pan <[email protected]>
---
Documentation/cgroups/freezer-subsystem.txt | 23 ++++
kernel/cgroup_freezer.c | 153 ++++++++++++++++++++++++++-
2 files changed, 174 insertions(+), 2 deletions(-)
diff --git a/Documentation/cgroups/freezer-subsystem.txt b/Documentation/cgroups/freezer-subsystem.txt
index 41f37fe..2022b32 100644
--- a/Documentation/cgroups/freezer-subsystem.txt
+++ b/Documentation/cgroups/freezer-subsystem.txt
@@ -100,3 +100,26 @@ things happens:
and returns EINVAL)
3) The tasks that blocked the cgroup from entering the "FROZEN"
state disappear from the cgroup's set of tasks.
+
+In embedded systems, it is desirable to manage group of applications
+for power saving. E.g. tasks that are not in the foreground may be
+frozen and unfrozen periodically to save power without affecting user
+experience. In this case, user/management software can attach tasks
+into freezer cgroup then specify duty ratio and period that the
+managed tasks are allowed to run.
+
+Usage example:
+Assuming freezer cgroup is already mounted, application being managed
+are included the "tasks" file node of the given freezer cgroup.
+To make the tasks frozen at 90% of the time every 5 seconds, do:
+
+[root@localhost ]# echo 90 > freezer.duty_ratio_pct
+[root@localhost ]# echo 5000 > freezer.period_ms
+
+After that, the application in this freezer cgroup will only be
+allowed to run at the following pattern.
+ __ __ __
+ | |<-- 90% frozen -->| | | |
+____| |__________________| |__________________| |_____
+
+ |<---- 5 seconds ---->|
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e7bebb7..aaa91ca 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -21,6 +21,7 @@
#include <linux/uaccess.h>
#include <linux/freezer.h>
#include <linux/seq_file.h>
+#include <linux/kthread.h>
enum freezer_state {
CGROUP_THAWED = 0,
@@ -28,12 +29,35 @@ enum freezer_state {
CGROUP_FROZEN,
};
+enum duty_ratio_params {
+ FREEZER_DUTY_RATIO = 0,
+ FREEZER_PERIOD,
+};
+
+struct freezer_toggle {
+ unsigned int enabled:1;
+ unsigned int freeze_thaw:1; /* 1: freeze 0: thaw */
+} __packed;
+
+struct freezer_duty {
+ u32 ratio; /* percentage of time frozen */
+ u32 period_pct_ms; /* one percent of the period in miliseconds */
+};
+
struct freezer {
struct cgroup_subsys_state css;
enum freezer_state state;
+ struct freezer_duty duty;
+ struct delayed_work freezer_work; /* work to duty-cycle a cgroup */
+ struct freezer_toggle toggle;
spinlock_t lock; /* protects _writes_ to state */
};
+static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer);
+static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer);
+static int freezer_change_state(struct cgroup *cgroup,
+ enum freezer_state goal_state);
+
static inline struct freezer *cgroup_freezer(
struct cgroup *cgroup)
{
@@ -63,6 +87,41 @@ int cgroup_freezing_or_frozen(struct task_struct *task)
return result;
}
+static DECLARE_WAIT_QUEUE_HEAD(freezer_wait);
+
+static void freezer_work_fn(struct work_struct *work)
+{
+ struct freezer *freezer;
+ unsigned long delay_jiffies = 0;
+ enum freezer_state goal_state;
+
+
+ freezer = container_of(work, struct freezer, freezer_work.work);
+ /* toggle between THAWED and FROZEN state.
+ * thaw if freezer->toggle.freeze_thaw = 0; freeze otherwise
+ * skip the first round if already in the target states.
+ */
+ if ((freezer->toggle.freeze_thaw && freezer->state == CGROUP_FROZEN) ||
+ (!freezer->toggle.freeze_thaw &&
+ freezer->state == CGROUP_THAWED)) {
+ delay_jiffies = 0;
+ goto exit_toggle;
+ } else if (freezer->toggle.freeze_thaw) {
+ goal_state = CGROUP_FROZEN;
+ delay_jiffies = msecs_to_jiffies(freezer->duty.ratio *
+ freezer->duty.period_pct_ms);
+ } else {
+ goal_state = CGROUP_THAWED;
+ delay_jiffies = msecs_to_jiffies((100 - freezer->duty.ratio) *
+ freezer->duty.period_pct_ms);
+ }
+ freezer_change_state(freezer->css.cgroup, goal_state);
+
+exit_toggle:
+ schedule_delayed_work(&freezer->freezer_work, delay_jiffies);
+ freezer->toggle.freeze_thaw ^= 1;
+}
+
/*
* cgroups_write_string() limits the size of freezer state strings to
* CGROUP_LOCAL_BUFFER_SIZE
@@ -150,7 +209,12 @@ static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
static void freezer_destroy(struct cgroup_subsys *ss,
struct cgroup *cgroup)
{
- kfree(cgroup_freezer(cgroup));
+ struct freezer *freezer;
+
+ freezer = cgroup_freezer(cgroup);
+ if (freezer->toggle.enabled)
+ cancel_delayed_work_sync(&freezer->freezer_work);
+ kfree(freezer);
}
/*
@@ -282,6 +346,16 @@ static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
return 0;
}
+static u64 freezer_read_duty_ratio(struct cgroup *cgroup, struct cftype *cft)
+{
+ return cgroup_freezer(cgroup)->duty.ratio;
+}
+
+static u64 freezer_read_period(struct cgroup *cgroup, struct cftype *cft)
+{
+ return cgroup_freezer(cgroup)->duty.period_pct_ms * 100;
+}
+
static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
{
struct cgroup_iter it;
@@ -353,6 +427,7 @@ static int freezer_write(struct cgroup *cgroup,
{
int retval;
enum freezer_state goal_state;
+ struct freezer *freezer;
if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
goal_state = CGROUP_THAWED;
@@ -360,7 +435,18 @@ static int freezer_write(struct cgroup *cgroup,
goal_state = CGROUP_FROZEN;
else
return -EINVAL;
-
+ /* we should stop duty ratio toggling if user wants to
+ * force change to a valid state.
+ */
+ freezer = cgroup_freezer(cgroup);
+ if (freezer->duty.period_pct_ms && freezer->duty.ratio < 100) {
+ if (freezer->toggle.enabled)
+ cancel_delayed_work_sync(&freezer->freezer_work);
+ freezer->duty.ratio = 0;
+ freezer->duty.period_pct_ms = 0;
+ freezer->toggle.enabled = 0;
+ pr_info("freezer state changed by user, stop duty ratio\n");
+ }
if (!cgroup_lock_live_group(cgroup))
return -ENODEV;
retval = freezer_change_state(cgroup, goal_state);
@@ -368,12 +454,75 @@ static int freezer_write(struct cgroup *cgroup,
return retval;
}
+#define FREEZER_KH_PREFIX "freezer_"
+static int freezer_write_param(struct cgroup *cgroup, struct cftype *cft,
+ u64 val)
+{
+ struct freezer *freezer;
+ int ret = 0;
+
+ freezer = cgroup_freezer(cgroup);
+
+ if (!cgroup_lock_live_group(cgroup))
+ return -ENODEV;
+
+ switch (cft->private) {
+ case FREEZER_DUTY_RATIO:
+ if (val >= 100) {
+ ret = -EINVAL;
+ goto exit;
+ }
+ freezer->duty.ratio = val;
+ break;
+ case FREEZER_PERIOD:
+ do_div(val, 100);
+ freezer->duty.period_pct_ms = val;
+ break;
+ default:
+ BUG();
+ }
+
+ /* only use delayed work when valid params are given. */
+ if (freezer->duty.ratio && freezer->duty.period_pct_ms &&
+ !freezer->toggle.enabled) {
+ pr_debug("starting duty ratio mode\n");
+ INIT_DELAYED_WORK(&freezer->freezer_work, freezer_work_fn);
+ freezer->toggle.enabled = 1;
+ schedule_delayed_work(&freezer->freezer_work, 0);
+ } else if ((!freezer->duty.ratio || !freezer->duty.period_pct_ms) &&
+ freezer->toggle.enabled) {
+ pr_debug("invalid param, stop duty ratio mode %p\n",
+ freezer->freezer_work.work.func);
+ cancel_delayed_work_sync(&freezer->freezer_work);
+ freezer->toggle.enabled = 0;
+ /* thaw the cgroup if we are not toggling */
+ freezer_change_state(freezer->css.cgroup, CGROUP_THAWED);
+
+ }
+exit:
+ cgroup_unlock();
+ return ret;
+}
+
static struct cftype files[] = {
{
.name = "state",
.read_seq_string = freezer_read,
.write_string = freezer_write,
},
+ {
+ .name = "duty_ratio_pct",
+ .private = FREEZER_DUTY_RATIO,
+ .read_u64 = freezer_read_duty_ratio,
+ .write_u64 = freezer_write_param,
+ },
+ {
+ .name = "period_ms",
+ .private = FREEZER_PERIOD,
+ .read_u64 = freezer_read_period,
+ .write_u64 = freezer_write_param,
+ },
+
};
static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
--
1.7.0.4
On Fri, Feb 11, 2011 at 11:10:44AM -0800, [email protected] wrote:
> From: Jacob Pan <[email protected]>
>
> Freezer subsystem is used to manage batch jobs which can start
> stop at the same time. However, sometime it is desirable to let
> the kernel manage the freezer state automatically with a given
> duty ratio.
> For example, if we want to reduce the time that backgroup apps
> are allowed to run we can put them into a freezer subsystem and
> set the kernel to turn them THAWED/FROZEN at given duty ratio.
>
> This patch introduces two file nodes under cgroup
> freezer.duty_ratio_pct and freezer.period_sec
Again: I don't think this is the right approach in the long term.
It would be better not to add this interface and instead enable the
cpu cgroup subsystem for non-rt tasks using a similar duty ratio
concept..
Nevertheless, I've added some feedback on the code for you here :).
>
> Usage example: set period to be 5 seconds and frozen duty ratio 90%
> [root@localhost aoa]# echo 90 > freezer.duty_ratio_pct
> [root@localhost aoa]# echo 5000 > freezer.period_ms
>
> Signed-off-by: Jacob Pan <[email protected]>
> ---
> Documentation/cgroups/freezer-subsystem.txt | 23 ++++
> kernel/cgroup_freezer.c | 153 ++++++++++++++++++++++++++-
> 2 files changed, 174 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/cgroups/freezer-subsystem.txt b/Documentation/cgroups/freezer-subsystem.txt
> index 41f37fe..2022b32 100644
> --- a/Documentation/cgroups/freezer-subsystem.txt
> +++ b/Documentation/cgroups/freezer-subsystem.txt
> @@ -100,3 +100,26 @@ things happens:
> and returns EINVAL)
> 3) The tasks that blocked the cgroup from entering the "FROZEN"
> state disappear from the cgroup's set of tasks.
> +
> +In embedded systems, it is desirable to manage group of applications
> +for power saving. E.g. tasks that are not in the foreground may be
> +frozen and unfrozen periodically to save power without affecting user
> +experience. In this case, user/management software can attach tasks
> +into freezer cgroup then specify duty ratio and period that the
> +managed tasks are allowed to run.
> +
> +Usage example:
> +Assuming freezer cgroup is already mounted, application being managed
> +are included the "tasks" file node of the given freezer cgroup.
> +To make the tasks frozen at 90% of the time every 5 seconds, do:
> +
> +[root@localhost ]# echo 90 > freezer.duty_ratio_pct
> +[root@localhost ]# echo 5000 > freezer.period_ms
> +
> +After that, the application in this freezer cgroup will only be
> +allowed to run at the following pattern.
> + __ __ __
> + | |<-- 90% frozen -->| | | |
> +____| |__________________| |__________________| |_____
> +
> + |<---- 5 seconds ---->|
So most of the time I've been reviewing this I managed to invert it!
I imagined "duty" meant the tasks were "on duty" ie runnable ie thawed.
But according this this documentation it's the opposite...
I've reviewed my review and now my comments are consistent with the
above. :) However it makes me wonder if there are better names which
would avoid this confusion.
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index e7bebb7..aaa91ca 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -21,6 +21,7 @@
> #include <linux/uaccess.h>
> #include <linux/freezer.h>
> #include <linux/seq_file.h>
> +#include <linux/kthread.h>
>
> enum freezer_state {
> CGROUP_THAWED = 0,
> @@ -28,12 +29,35 @@ enum freezer_state {
> CGROUP_FROZEN,
> };
>
> +enum duty_ratio_params {
> + FREEZER_DUTY_RATIO = 0,
> + FREEZER_PERIOD,
> +};
> +
> +struct freezer_toggle {
> + unsigned int enabled:1;
> + unsigned int freeze_thaw:1; /* 1: freeze 0: thaw */
> +} __packed;
> +
> +struct freezer_duty {
> + u32 ratio; /* percentage of time frozen */
> + u32 period_pct_ms; /* one percent of the period in miliseconds */
> +};
I'd rather see you merge these two structures -- I don't see the value
of keeping them separate nor of packing the struct. You could also merge
the work item in there:
struct freezer_duty {
struct delayed_work freezer_work; /* work to duty-cycle a cgroup */
u32 ratio; /* percentage of time frozen */
u32 period_pct_ms; /* one percent of the period in miliseconds */
unsigned int enabled:1;
unsigned int freeze_thaw:1; /* 1: freeze 0: thaw */
};
(I'm going to make the rest of my comments without assuming you've done
this because it'll make them easier to follow given the context)
> +
> struct freezer {
> struct cgroup_subsys_state css;
> enum freezer_state state;
> + struct freezer_duty duty;
> + struct delayed_work freezer_work; /* work to duty-cycle a cgroup */
> + struct freezer_toggle toggle;
> spinlock_t lock; /* protects _writes_ to state */
> };
>
> +static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer);
> +static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer);
> +static int freezer_change_state(struct cgroup *cgroup,
> + enum freezer_state goal_state);
> +
> static inline struct freezer *cgroup_freezer(
> struct cgroup *cgroup)
> {
> @@ -63,6 +87,41 @@ int cgroup_freezing_or_frozen(struct task_struct *task)
> return result;
> }
>
> +static DECLARE_WAIT_QUEUE_HEAD(freezer_wait);
> +
> +static void freezer_work_fn(struct work_struct *work)
> +{
> + struct freezer *freezer;
> + unsigned long delay_jiffies = 0;
> + enum freezer_state goal_state;
> +
Looking better. There are alot of field accesses here which can race
with writes to the cgroup's duty ratio and period files. They should be
protected. Perhaps we can reuse the freezer spin lock. That also
has the benefit that we can eliminate the toggle.freeze_thaw bit I
think:
> +
> + freezer = container_of(work, struct freezer, freezer_work.work);
> + /* toggle between THAWED and FROZEN state.
> + * thaw if freezer->toggle.freeze_thaw = 0; freeze otherwise
> + * skip the first round if already in the target states.
> + */
spin_lock(&freezer->lock);
> + if ((freezer->toggle.freeze_thaw && freezer->state == CGROUP_FROZEN) ||
> + (!freezer->toggle.freeze_thaw &&
> + freezer->state == CGROUP_THAWED)) {
> + delay_jiffies = 0;
This looks wrong. We should never schedule freezer work delayed by 0
jiffies -- even if the delayed work API allows it. With 0-length delays
I'd worry that we could peg the CPU in an obscure infinite loop.
I think you can safely eliminate this block and the "exit_toggle" label.
> + goto exit_toggle;
> + } else if (freezer->toggle.freeze_thaw) {
if (freezer->state == CGROUP_THAWED) {
> + goal_state = CGROUP_FROZEN;
> + delay_jiffies = msecs_to_jiffies(freezer->duty.ratio *
> + freezer->duty.period_pct_ms);
> + } else {
> + goal_state = CGROUP_THAWED;
> + delay_jiffies = msecs_to_jiffies((100 - freezer->duty.ratio) *
> + freezer->duty.period_pct_ms);
> + }
> + freezer_change_state(freezer->css.cgroup, goal_state);
__freezer_change_state(freezer->css.cgroup, goal_state);
spin_unlock(&freezer->lock);
(where the __freezer_change_state() function expects to already have the
freezer lock -- you can make that your first patch and this your second)
But you ought to double check the lock ordering, may-sleep, and whether
the _irq variants are correct.
> +
> +exit_toggle:
> + schedule_delayed_work(&freezer->freezer_work, delay_jiffies);
> + freezer->toggle.freeze_thaw ^= 1;
This looks wrong. It looks like there could be a race between the next
scheduled work and the toggling of the freeze_thaw value. This race
would cause the cgroup to miss one or more duty cycles. You'd have
to re-order these two lines and probably need an smp barrier of one
sort or another between them.
Of course if you use locking and eliminate the toggle.freeze_thaw field
as I've suggested then you can ignore this.
> +}
> +
> /*
> * cgroups_write_string() limits the size of freezer state strings to
> * CGROUP_LOCAL_BUFFER_SIZE
> @@ -150,7 +209,12 @@ static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
> static void freezer_destroy(struct cgroup_subsys *ss,
> struct cgroup *cgroup)
> {
> - kfree(cgroup_freezer(cgroup));
> + struct freezer *freezer;
> +
> + freezer = cgroup_freezer(cgroup);
> + if (freezer->toggle.enabled)
> + cancel_delayed_work_sync(&freezer->freezer_work);
> + kfree(freezer);
> }
>
> /*
> @@ -282,6 +346,16 @@ static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
> return 0;
> }
>
> +static u64 freezer_read_duty_ratio(struct cgroup *cgroup, struct cftype *cft)
> +{
> + return cgroup_freezer(cgroup)->duty.ratio;
> +}
> +
> +static u64 freezer_read_period(struct cgroup *cgroup, struct cftype *cft)
> +{
> + return cgroup_freezer(cgroup)->duty.period_pct_ms * 100;
> +}
> +
> static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
> {
> struct cgroup_iter it;
> @@ -353,6 +427,7 @@ static int freezer_write(struct cgroup *cgroup,
> {
> int retval;
> enum freezer_state goal_state;
> + struct freezer *freezer;
>
> if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
> goal_state = CGROUP_THAWED;
> @@ -360,7 +435,18 @@ static int freezer_write(struct cgroup *cgroup,
> goal_state = CGROUP_FROZEN;
> else
> return -EINVAL;
> -
> + /* we should stop duty ratio toggling if user wants to
> + * force change to a valid state.
> + */
> + freezer = cgroup_freezer(cgroup);
> + if (freezer->duty.period_pct_ms && freezer->duty.ratio < 100) {
If duty.ratio is 100 then the delayed work should be cancelled too.
In fact it doesn't matter what the duty.ratio or period_pct_ms are --
writes to this file should always disable the duty cycle. Thus
you can omit the above if () and do this:
> + if (freezer->toggle.enabled)
{
> + cancel_delayed_work_sync(&freezer->freezer_work);
> + freezer->duty.ratio = 0;
Actually, shouldn't this be 0 if the cgroup is going to be thawed and
100 if it's going to be frozen?
> + freezer->duty.period_pct_ms = 0;
I think this should always be a non-zero value -- even when duty
cycling is disabled. Perhaps:
freezer->duty.period_pct_ms = 1000/100;
So it's clear the default period is 1000ms and one percent of it is 10ms.
(NOTE: To make it always non-zero you also need to add one line to the
cgroup initialization code in freezer_create()).
> + freezer->toggle.enabled = 0;
> + pr_info("freezer state changed by user, stop duty ratio\n");
nit: I don't think this pr_info() is terribly useful.
> + }
> if (!cgroup_lock_live_group(cgroup))
> return -ENODEV;
> retval = freezer_change_state(cgroup, goal_state);
> @@ -368,12 +454,75 @@ static int freezer_write(struct cgroup *cgroup,
> return retval;
> }
>
> +#define FREEZER_KH_PREFIX "freezer_"
This #define is unused.
> +static int freezer_write_param(struct cgroup *cgroup, struct cftype *cft,
> + u64 val)
> +{
> + struct freezer *freezer;
> + int ret = 0;
> +
> + freezer = cgroup_freezer(cgroup);
> +
> + if (!cgroup_lock_live_group(cgroup))
> + return -ENODEV;
Because the delayed work function does not lock the cgroup this whole
function can race with the delayed work. So we need to be careful about how
we set/test all of these new fields -- we probably want to reuse the
freezer state lock for this so I've sprinkled some lock/unlock bits with
my comments below.
> +
> + switch (cft->private) {
> + case FREEZER_DUTY_RATIO:
> + if (val >= 100) {
ratio == 100 ought to be allowed too.
> + ret = -EINVAL;
> + goto exit;
> + }
Add:
spin_lock_irq(&freezer->lock);
> + freezer->duty.ratio = val;
Because this can race with the delayed work.
> + break;
> + case FREEZER_PERIOD:
> + do_div(val, 100);
> + freezer->duty.period_pct_ms = val;
This can race with the delayed work. Also I think that a 0ms period_pct_ms
should be disallowed. Otherwise all the work delays go to zero and we'll
probably peg the CPU so that it's just spinning the freezer state between
FROZEN and THAWED and doing nothing else.
Finally, I wonder if a 64-bit value is really necessary -- is a period
longer than roughly 50 days really necessary?
In summary, couldn't you just do something like:
if ((val < 100) || (val > UINT_MAX)) {
/* Too much time or may have rounded down to 0 */
ret = -EINVAL;
goto exit;
}
val = (unsigned int)val / 100;
spin_lock_irq(&freezer->lock);
freezer->duty.period_pct_ms = val;
> + break;
> + default:
> + BUG();
> + }
> +
> + /* only use delayed work when valid params are given. */
> + if (freezer->duty.ratio && freezer->duty.period_pct_ms &&
> + !freezer->toggle.enabled) {
> + pr_debug("starting duty ratio mode\n");
> + INIT_DELAYED_WORK(&freezer->freezer_work, freezer_work_fn);
> + freezer->toggle.enabled = 1;
> + schedule_delayed_work(&freezer->freezer_work, 0);
> + } else if ((!freezer->duty.ratio || !freezer->duty.period_pct_ms) &&
> + freezer->toggle.enabled) {
> + pr_debug("invalid param, stop duty ratio mode %p\n",
> + freezer->freezer_work.work.func);
> + cancel_delayed_work_sync(&freezer->freezer_work);
> + freezer->toggle.enabled = 0;
> + /* thaw the cgroup if we are not toggling */
> + freezer_change_state(freezer->css.cgroup, CGROUP_THAWED);
> +
> + }
I don't think this is as readable as (assuming the change above to disallow
setting period_pct_ms to 0):
if (freezer->duty.ratio == 100) {
freezer_disable_duty_cycling(freezer); /* see helper below */
__freezer_change_state(freezer->css.cgroup, CGROUP_FROZEN);
} else if (freezer->duty.ratio == 0) {
freezer_disable_duty_cycling(freezer);
__freezer_change_state(freezer->css.cgroup, CGROUP_THAWED);
} else {
if (freezer->toggle.enabled)
goto exit; /* Already enabled */
INIT_DELAYED_WORK(&freezer->freezer_work, freezer_work_fn);
freezer->toggle.enabled = 1;
schedule_delayed_work(&freezer->freezer_work, 0);
}
spin_unlock_irq(&freezer->lock);
Where the helper is:
static void freezer_disable_duty_cycling(struct freezer *freezer)
{
if (freezer->toggle.enabled) {
cancel_delayed_work_sync(&freezer->freezer_work);
freezer->toggle.enabled = 0;
}
}
which could also be called from freezer_write() I think.
Cheers,
-Matt Helsley
On Sat, 12 Feb 2011 15:29:07 -0800
Matt Helsley <[email protected]> wrote:
> On Fri, Feb 11, 2011 at 11:10:44AM -0800, [email protected] wrote:
> > From: Jacob Pan <[email protected]>
> >
> > Freezer subsystem is used to manage batch jobs which can start
> > stop at the same time. However, sometime it is desirable to let
> > the kernel manage the freezer state automatically with a given
> > duty ratio.
> > For example, if we want to reduce the time that backgroup apps
> > are allowed to run we can put them into a freezer subsystem and
> > set the kernel to turn them THAWED/FROZEN at given duty ratio.
> >
> > This patch introduces two file nodes under cgroup
> > freezer.duty_ratio_pct and freezer.period_sec
>
> Again: I don't think this is the right approach in the long term.
> It would be better not to add this interface and instead enable the
> cpu cgroup subsystem for non-rt tasks using a similar duty ratio
> concept..
>
> Nevertheless, I've added some feedback on the code for you here :).
>
AFAIK, there was a work for bandwidth control in CFS.
http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-10/msg04335.html
I tested this and worked fine. This schduler approach seems better for
my purpose to limit bandwidth of apprications rather than freezer.
BTW, isn't period_sec too large ?
Thanks,
-Kame
On 2/13/2011 4:44 PM, KAMEZAWA Hiroyuki wrote:
> On Sat, 12 Feb 2011 15:29:07 -0800
> Matt Helsley<[email protected]> wrote:
>
>> On Fri, Feb 11, 2011 at 11:10:44AM -0800, [email protected] wrote:
>>> From: Jacob Pan<[email protected]>
>>>
>>> Freezer subsystem is used to manage batch jobs which can start
>>> stop at the same time. However, sometime it is desirable to let
>>> the kernel manage the freezer state automatically with a given
>>> duty ratio.
>>> For example, if we want to reduce the time that backgroup apps
>>> are allowed to run we can put them into a freezer subsystem and
>>> set the kernel to turn them THAWED/FROZEN at given duty ratio.
>>>
>>> This patch introduces two file nodes under cgroup
>>> freezer.duty_ratio_pct and freezer.period_sec
>> Again: I don't think this is the right approach in the long term.
>> It would be better not to add this interface and instead enable the
>> cpu cgroup subsystem for non-rt tasks using a similar duty ratio
>> concept..
>>
>> Nevertheless, I've added some feedback on the code for you here :).
>>
> AFAIK, there was a work for bandwidth control in CFS.
>
> http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-10/msg04335.html
>
> I tested this and worked fine. This schduler approach seems better for
> my purpose to limit bandwidth of apprications rather than freezer.
for our purpose, it's not about bandwidth.
it's about making sure the class of apps don't run for a long period
(30-second range) of time.
On Sat, 12 Feb 2011 15:29:07 -0800
Matt Helsley <[email protected]> wrote:
> On Fri, Feb 11, 2011 at 11:10:44AM -0800,
> [email protected] wrote:
> > From: Jacob Pan <[email protected]>
> >
> > Freezer subsystem is used to manage batch jobs which can start
> > stop at the same time. However, sometime it is desirable to let
> > the kernel manage the freezer state automatically with a given
> > duty ratio.
> > For example, if we want to reduce the time that backgroup apps
> > are allowed to run we can put them into a freezer subsystem and
> > set the kernel to turn them THAWED/FROZEN at given duty ratio.
> >
> > This patch introduces two file nodes under cgroup
> > freezer.duty_ratio_pct and freezer.period_sec
>
> Again: I don't think this is the right approach in the long term.
> It would be better not to add this interface and instead enable the
> cpu cgroup subsystem for non-rt tasks using a similar duty ratio
> concept..
>
> Nevertheless, I've added some feedback on the code for you here :).
>
Thanks for the thorough review, really appreciated.
> >
> > Usage example: set period to be 5 seconds and frozen duty ratio 90%
> > [root@localhost aoa]# echo 90 > freezer.duty_ratio_pct
> > [root@localhost aoa]# echo 5000 > freezer.period_ms
> >
> > Signed-off-by: Jacob Pan <[email protected]>
> > ---
> > Documentation/cgroups/freezer-subsystem.txt | 23 ++++
> > kernel/cgroup_freezer.c | 153
> > ++++++++++++++++++++++++++- 2 files changed, 174 insertions(+), 2
> > deletions(-)
> >
> > diff --git a/Documentation/cgroups/freezer-subsystem.txt
> > b/Documentation/cgroups/freezer-subsystem.txt index
> > 41f37fe..2022b32 100644 ---
> > a/Documentation/cgroups/freezer-subsystem.txt +++
> > b/Documentation/cgroups/freezer-subsystem.txt @@ -100,3 +100,26 @@
> > things happens: and returns EINVAL)
> > 3) The tasks that blocked the cgroup from entering the
> > "FROZEN" state disappear from the cgroup's set of tasks.
> > +
> > +In embedded systems, it is desirable to manage group of
> > applications +for power saving. E.g. tasks that are not in the
> > foreground may be +frozen and unfrozen periodically to save power
> > without affecting user +experience. In this case, user/management
> > software can attach tasks +into freezer cgroup then specify duty
> > ratio and period that the +managed tasks are allowed to run.
> > +
> > +Usage example:
> > +Assuming freezer cgroup is already mounted, application being
> > managed +are included the "tasks" file node of the given freezer
> > cgroup. +To make the tasks frozen at 90% of the time every 5
> > seconds, do: +
> > +[root@localhost ]# echo 90 > freezer.duty_ratio_pct
> > +[root@localhost ]# echo 5000 > freezer.period_ms
> > +
> > +After that, the application in this freezer cgroup will only be
> > +allowed to run at the following pattern.
> > + __ __ __
> > + | |<-- 90% frozen -->| | | |
> > +____| |__________________| |__________________| |_____
> > +
> > + |<---- 5 seconds ---->|
>
> So most of the time I've been reviewing this I managed to invert it!
> I imagined "duty" meant the tasks were "on duty" ie runnable ie
> thawed. But according this this documentation it's the opposite...
>
My logic is that since this is a freezer, so positive logic should be
frozen instead of thaw.
> I've reviewed my review and now my comments are consistent with the
> above. :) However it makes me wonder if there are better names which
> would avoid this confusion.
>
How about frozen_time_pct?
> > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> > index e7bebb7..aaa91ca 100644
> > --- a/kernel/cgroup_freezer.c
> > +++ b/kernel/cgroup_freezer.c
> > @@ -21,6 +21,7 @@
> > #include <linux/uaccess.h>
> > #include <linux/freezer.h>
> > #include <linux/seq_file.h>
> > +#include <linux/kthread.h>
> >
> > enum freezer_state {
> > CGROUP_THAWED = 0,
> > @@ -28,12 +29,35 @@ enum freezer_state {
> > CGROUP_FROZEN,
> > };
> >
> > +enum duty_ratio_params {
> > + FREEZER_DUTY_RATIO = 0,
> > + FREEZER_PERIOD,
> > +};
> > +
> > +struct freezer_toggle {
> > + unsigned int enabled:1;
> > + unsigned int freeze_thaw:1; /* 1: freeze 0: thaw */
> > +} __packed;
> > +
> > +struct freezer_duty {
> > + u32 ratio; /* percentage of time frozen */
> > + u32 period_pct_ms; /* one percent of the period in
> > miliseconds */ +};
>
> I'd rather see you merge these two structures -- I don't see the value
> of keeping them separate nor of packing the struct. You could also
> merge the work item in there:
>
> struct freezer_duty {
> struct delayed_work freezer_work; /* work to duty-cycle a
> cgroup */
>
> u32 ratio; /* percentage of time frozen */
> u32 period_pct_ms; /* one percent of the period in
> miliseconds */ unsigned int enabled:1;
> unsigned int freeze_thaw:1; /* 1: freeze 0: thaw */
> };
>
> (I'm going to make the rest of my comments without assuming you've
> done this because it'll make them easier to follow given the context)
>
I don't have strong preference, but it seems more logical to merge all
toggling related structures. I will change that.
> > +
> > struct freezer {
> > struct cgroup_subsys_state css;
> > enum freezer_state state;
> > + struct freezer_duty duty;
> > + struct delayed_work freezer_work; /* work to duty-cycle a
> > cgroup */
> > + struct freezer_toggle toggle;
> > spinlock_t lock; /* protects _writes_ to state */
> > };
> >
> > +static int try_to_freeze_cgroup(struct cgroup *cgroup, struct
> > freezer *freezer); +static void unfreeze_cgroup(struct cgroup
> > *cgroup, struct freezer *freezer); +static int
> > freezer_change_state(struct cgroup *cgroup,
> > + enum freezer_state goal_state);
> > +
> > static inline struct freezer *cgroup_freezer(
> > struct cgroup *cgroup)
> > {
> > @@ -63,6 +87,41 @@ int cgroup_freezing_or_frozen(struct task_struct
> > *task) return result;
> > }
> >
> > +static DECLARE_WAIT_QUEUE_HEAD(freezer_wait);
> > +
> > +static void freezer_work_fn(struct work_struct *work)
> > +{
> > + struct freezer *freezer;
> > + unsigned long delay_jiffies = 0;
> > + enum freezer_state goal_state;
> > +
>
> Looking better. There are alot of field accesses here which can race
> with writes to the cgroup's duty ratio and period files. They should
> be protected. Perhaps we can reuse the freezer spin lock. That also
> has the benefit that we can eliminate the toggle.freeze_thaw bit I
> think:
>
I did think about the race, it does exist. but in practice. My thought
was that since freezer_change_state() holds the spin_lock of the
freezer, the race with writes to params are harmless, it just means the
new period or ratio will take effect in the next period.
In terms of using freezer spin lock to eliminate toggle flag, I am not
sure if i know how to do that. Are you suggesting based on whether the
spin lock is taken or not, we can decide the toggle? but the freeze
spin lock is used by other functions as well not just the delay work
here. I guess I have missed something.
> > +
> > + freezer = container_of(work, struct freezer,
> > freezer_work.work);
> > + /* toggle between THAWED and FROZEN state.
> > + * thaw if freezer->toggle.freeze_thaw = 0; freeze
> > otherwise
> > + * skip the first round if already in the target states.
> > + */
>
> spin_lock(&freezer->lock);
>
> > + if ((freezer->toggle.freeze_thaw && freezer->state ==
> > CGROUP_FROZEN) ||
> > + (!freezer->toggle.freeze_thaw &&
> > + freezer->state == CGROUP_THAWED)) {
> > + delay_jiffies = 0;
>
> This looks wrong. We should never schedule freezer work delayed by 0
> jiffies -- even if the delayed work API allows it. With 0-length
> delays I'd worry that we could peg the CPU in an obscure infinite
> loop.
>
> I think you can safely eliminate this block and the "exit_toggle"
> label.
>
Good point. My initial thought was that since the period for targeted
usage is quite long, e.g. 30 sec., we want to start the duty ratio
right away. But that shouldn't matter since we already schedule work
based on the new ratio/period.
> > + goto exit_toggle;
> > + } else if (freezer->toggle.freeze_thaw) {
>
> if (freezer->state == CGROUP_THAWED) {
>
> > + goal_state = CGROUP_FROZEN;
> > + delay_jiffies =
> > msecs_to_jiffies(freezer->duty.ratio *
> > +
> > freezer->duty.period_pct_ms);
> > + } else {
> > + goal_state = CGROUP_THAWED;
> > + delay_jiffies = msecs_to_jiffies((100 -
> > freezer->duty.ratio) *
> > +
> > freezer->duty.period_pct_ms);
> > + }
> > + freezer_change_state(freezer->css.cgroup, goal_state);
>
> __freezer_change_state(freezer->css.cgroup, goal_state);
> spin_unlock(&freezer->lock);
>
> (where the __freezer_change_state() function expects to already have
> the freezer lock -- you can make that your first patch and this your
> second)
>
> But you ought to double check the lock ordering, may-sleep, and
> whether the _irq variants are correct.
>
I agree with the change to deal with race but again, I don't see the
harm of the race other than delaying one period. If the user has to
change period and duty ratio separately, there will always be a window
of unwanted params unless user disable it first.
Can you please explain the problem might be caused by the race.
> > +
> > +exit_toggle:
> > + schedule_delayed_work(&freezer->freezer_work,
> > delay_jiffies);
> > + freezer->toggle.freeze_thaw ^= 1;
>
> This looks wrong. It looks like there could be a race between the next
> scheduled work and the toggling of the freeze_thaw value. This race
> would cause the cgroup to miss one or more duty cycles. You'd have
> to re-order these two lines and probably need an smp barrier of one
> sort or another between them.
>
I will fix that. good point.
> Of course if you use locking and eliminate the toggle.freeze_thaw
> field as I've suggested then you can ignore this.
>
same as before, not sure how to reuse the freezer spin lock for this.
can you please explain.
> > +}
> > +
> > /*
> > * cgroups_write_string() limits the size of freezer state strings
> > to
> > * CGROUP_LOCAL_BUFFER_SIZE
> > @@ -150,7 +209,12 @@ static struct cgroup_subsys_state
> > *freezer_create(struct cgroup_subsys *ss, static void
> > freezer_destroy(struct cgroup_subsys *ss, struct cgroup *cgroup)
> > {
> > - kfree(cgroup_freezer(cgroup));
> > + struct freezer *freezer;
> > +
> > + freezer = cgroup_freezer(cgroup);
> > + if (freezer->toggle.enabled)
> > + cancel_delayed_work_sync(&freezer->freezer_work);
> > + kfree(freezer);
> > }
> >
> > /*
> > @@ -282,6 +346,16 @@ static int freezer_read(struct cgroup *cgroup,
> > struct cftype *cft, return 0;
> > }
> >
> > +static u64 freezer_read_duty_ratio(struct cgroup *cgroup, struct
> > cftype *cft) +{
> > + return cgroup_freezer(cgroup)->duty.ratio;
> > +}
> > +
> > +static u64 freezer_read_period(struct cgroup *cgroup, struct
> > cftype *cft) +{
> > + return cgroup_freezer(cgroup)->duty.period_pct_ms * 100;
> > +}
> > +
> > static int try_to_freeze_cgroup(struct cgroup *cgroup, struct
> > freezer *freezer) {
> > struct cgroup_iter it;
> > @@ -353,6 +427,7 @@ static int freezer_write(struct cgroup *cgroup,
> > {
> > int retval;
> > enum freezer_state goal_state;
> > + struct freezer *freezer;
> >
> > if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
> > goal_state = CGROUP_THAWED;
> > @@ -360,7 +435,18 @@ static int freezer_write(struct cgroup *cgroup,
> > goal_state = CGROUP_FROZEN;
> > else
> > return -EINVAL;
> > -
> > + /* we should stop duty ratio toggling if user wants to
> > + * force change to a valid state.
> > + */
> > + freezer = cgroup_freezer(cgroup);
> > + if (freezer->duty.period_pct_ms && freezer->duty.ratio <
> > 100) {
>
> If duty.ratio is 100 then the delayed work should be cancelled too.
> In fact it doesn't matter what the duty.ratio or period_pct_ms are --
> writes to this file should always disable the duty cycle. Thus
> you can omit the above if () and do this:
>
> > + if (freezer->toggle.enabled)
>
agreed, i will fix it.
> {
>
> > +
> > cancel_delayed_work_sync(&freezer->freezer_work);
> > + freezer->duty.ratio = 0;
>
> Actually, shouldn't this be 0 if the cgroup is going to be thawed and
> 100 if it's going to be frozen?
>
I am using 0 as an invalid value when toggle is not enabled. perhaps i
should introduce -1 such that when user override occurs we just do
freezer->toggle.enabled = 0;
freezer->duty.ratio = -1;
freezer->duty.period_pct_ms = -1;
then we can allow and or 100% where both will turn off toggle as well.
> > + freezer->duty.period_pct_ms = 0;
>
> I think this should always be a non-zero value -- even when duty
> cycling is disabled. Perhaps:
>
> freezer->duty.period_pct_ms = 1000/100;
>
> So it's clear the default period is 1000ms and one percent of it is
> 10ms.
>
> (NOTE: To make it always non-zero you also need to add one line to the
> cgroup initialization code in freezer_create()).
how about -1 as suggested above.
>
> > + freezer->toggle.enabled = 0;
> > + pr_info("freezer state changed by user, stop duty
> > ratio\n");
>
> nit: I don't think this pr_info() is terribly useful.
>
I will make it pr_debug instead.
> > + }
> > if (!cgroup_lock_live_group(cgroup))
> > return -ENODEV;
> > retval = freezer_change_state(cgroup, goal_state);
> > @@ -368,12 +454,75 @@ static int freezer_write(struct cgroup
> > *cgroup, return retval;
> > }
> >
> > +#define FREEZER_KH_PREFIX "freezer_"
>
> This #define is unused.
fixed in v8
>
> > +static int freezer_write_param(struct cgroup *cgroup, struct
> > cftype *cft,
> > + u64 val)
> > +{
> > + struct freezer *freezer;
> > + int ret = 0;
> > +
> > + freezer = cgroup_freezer(cgroup);
> > +
> > + if (!cgroup_lock_live_group(cgroup))
> > + return -ENODEV;
>
> Because the delayed work function does not lock the cgroup this whole
> function can race with the delayed work. So we need to be careful
> about how we set/test all of these new fields -- we probably want to
> reuse the freezer state lock for this so I've sprinkled some
> lock/unlock bits with my comments below.
>
same as before, I don't see the harm of the race.
> > +
> > + switch (cft->private) {
> > + case FREEZER_DUTY_RATIO:
> > + if (val >= 100) {
>
> ratio == 100 ought to be allowed too.
Ok, 100% frozen would be equivalent to echo FROZEN > freezer.state. I
will document these corner cases. I think as long as these behaviors
are documented well so that user can get the anticipated results, the
interface does matter that much.
>
> > + ret = -EINVAL;
> > + goto exit;
> > + }
>
> Add:
>
> spin_lock_irq(&freezer->lock);
>
> > + freezer->duty.ratio = val;
>
> Because this can race with the delayed work.
>
> > + break;
> > + case FREEZER_PERIOD:
> > + do_div(val, 100);
> > + freezer->duty.period_pct_ms = val;
>
> This can race with the delayed work. Also I think that a 0ms
> period_pct_ms should be disallowed. Otherwise all the work delays go
> to zero and we'll probably peg the CPU so that it's just spinning the
> freezer state between FROZEN and THAWED and doing nothing else.
>
0 or low number of period is dangerous for reason as you mentioned,
I think I should move back to one second resolution. Especially, we are
using common workqueue now.
> Finally, I wonder if a 64-bit value is really necessary -- is a period
> longer than roughly 50 days really necessary?
>
> In summary, couldn't you just do something like:
>
> if ((val < 100) || (val > UINT_MAX)) {
> /* Too much time or may have rounded down to
> 0 */ ret = -EINVAL;
> goto exit;
> }
> val = (unsigned int)val / 100;
> spin_lock_irq(&freezer->lock);
> freezer->duty.period_pct_ms = val;
>
u64 is not needed. I will fix that.
> > + break;
> > + default:
> > + BUG();
> > + }
> > +
> > + /* only use delayed work when valid params are given. */
> > + if (freezer->duty.ratio && freezer->duty.period_pct_ms &&
> > + !freezer->toggle.enabled) {
> > + pr_debug("starting duty ratio mode\n");
> > + INIT_DELAYED_WORK(&freezer->freezer_work,
> > freezer_work_fn);
> > + freezer->toggle.enabled = 1;
> > + schedule_delayed_work(&freezer->freezer_work, 0);
> > + } else if ((!freezer->duty.ratio
> > || !freezer->duty.period_pct_ms) &&
> > + freezer->toggle.enabled) {
> > + pr_debug("invalid param, stop duty ratio mode
> > %p\n",
> > + freezer->freezer_work.work.func);
> > + cancel_delayed_work_sync(&freezer->freezer_work);
> > + freezer->toggle.enabled = 0;
> > + /* thaw the cgroup if we are not toggling */
> > + freezer_change_state(freezer->css.cgroup,
> > CGROUP_THAWED); +
> > + }
>
> I don't think this is as readable as (assuming the change above to
> disallow setting period_pct_ms to 0):
>
> if (freezer->duty.ratio == 100) {
> freezer_disable_duty_cycling(freezer); /* see helper
> below */ __freezer_change_state(freezer->css.cgroup, CGROUP_FROZEN);
> } else if (freezer->duty.ratio == 0) {
> freezer_disable_duty_cycling(freezer);
> __freezer_change_state(freezer->css.cgroup,
> CGROUP_THAWED); } else {
> if (freezer->toggle.enabled)
> goto exit; /* Already enabled */
> INIT_DELAYED_WORK(&freezer->freezer_work,
> freezer_work_fn); freezer->toggle.enabled = 1;
> schedule_delayed_work(&freezer->freezer_work, 0);
> }
> spin_unlock_irq(&freezer->lock);
>
> Where the helper is:
>
> static void freezer_disable_duty_cycling(struct freezer *freezer)
> {
> if (freezer->toggle.enabled) {
> cancel_delayed_work_sync(&freezer->freezer_work);
> freezer->toggle.enabled = 0;
> }
> }
>
> which could also be called from freezer_write() I think.
>
Other than my doubt on spin lock i.e. __freezer_change_state(), i think
the helper function does make it cleaner.
Thanks again,
Jacob
On Mon, Feb 14, 2011 at 11:41:42AM -0800, jacob pan wrote:
> On Sat, 12 Feb 2011 15:29:07 -0800
> Matt Helsley <[email protected]> wrote:
>
> > On Fri, Feb 11, 2011 at 11:10:44AM -0800,
> > [email protected] wrote:
> > > From: Jacob Pan <[email protected]>
<snip>
> > > cgroup. +To make the tasks frozen at 90% of the time every 5
> > > seconds, do: +
> > > +[root@localhost ]# echo 90 > freezer.duty_ratio_pct
> > > +[root@localhost ]# echo 5000 > freezer.period_ms
> > > +
> > > +After that, the application in this freezer cgroup will only be
> > > +allowed to run at the following pattern.
> > > + __ __ __
> > > + | |<-- 90% frozen -->| | | |
> > > +____| |__________________| |__________________| |_____
> > > +
> > > + |<---- 5 seconds ---->|
> >
> > So most of the time I've been reviewing this I managed to invert it!
> > I imagined "duty" meant the tasks were "on duty" ie runnable ie
> > thawed. But according this this documentation it's the opposite...
> >
> My logic is that since this is a freezer, so positive logic should be
> frozen instead of thaw.
Yup, I figured as much. That's the reason I didn't ask you to swap the
meaning of the ratio values.
> > I've reviewed my review and now my comments are consistent with the
> > above. :) However it makes me wonder if there are better names which
> > would avoid this confusion.
> >
> How about frozen_time_pct?
Much better! nit: I don't know if _pct is obvious to everyone but it only
takes 4 more characters to make it so..
> > > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
<snip>
> > > +static void freezer_work_fn(struct work_struct *work)
> > > +{
> > > + struct freezer *freezer;
> > > + unsigned long delay_jiffies = 0;
> > > + enum freezer_state goal_state;
> > > +
> >
> > Looking better. There are alot of field accesses here which can race
> > with writes to the cgroup's duty ratio and period files. They should
> > be protected. Perhaps we can reuse the freezer spin lock. That also
> > has the benefit that we can eliminate the toggle.freeze_thaw bit I
> > think:
> >
> I did think about the race, it does exist. but in practice. My thought
> was that since freezer_change_state() holds the spin_lock of the
> freezer, the race with writes to params are harmless, it just means the
> new period or ratio will take effect in the next period.
I considered this but didn't like the idea of relying on it. More below.
> In terms of using freezer spin lock to eliminate toggle flag, I am not
> sure if i know how to do that. Are you suggesting based on whether the
> spin lock is taken or not, we can decide the toggle? but the freeze
> spin lock is used by other functions as well not just the delay work
> here. I guess I have missed something.
I was thinking that with the lock held you can check the state variable
and just do the "opposite" of what it indicates:
state TODO
FROZEN THAWED
FREEZING THAWED
THAWED FROZEN
Then you don't need the separate bit to indicate which state it should
try to change to next.
> > > +
> > > + freezer = container_of(work, struct freezer,
> > > freezer_work.work);
> > > + /* toggle between THAWED and FROZEN state.
> > > + * thaw if freezer->toggle.freeze_thaw = 0; freeze
> > > otherwise
> > > + * skip the first round if already in the target states.
> > > + */
> >
> > spin_lock(&freezer->lock);
> >
> > > + if ((freezer->toggle.freeze_thaw && freezer->state ==
> > > CGROUP_FROZEN) ||
> > > + (!freezer->toggle.freeze_thaw &&
> > > + freezer->state == CGROUP_THAWED)) {
> > > + delay_jiffies = 0;
> >
> > This looks wrong. We should never schedule freezer work delayed by 0
> > jiffies -- even if the delayed work API allows it. With 0-length
> > delays I'd worry that we could peg the CPU in an obscure infinite
> > loop.
> >
> > I think you can safely eliminate this block and the "exit_toggle"
> > label.
> >
> Good point. My initial thought was that since the period for targeted
> usage is quite long, e.g. 30 sec., we want to start the duty ratio
> right away. But that shouldn't matter since we already schedule work
> based on the new ratio/period.
> > > + goto exit_toggle;
> > > + } else if (freezer->toggle.freeze_thaw) {
> >
> > if (freezer->state == CGROUP_THAWED) {
> >
> > > + goal_state = CGROUP_FROZEN;
> > > + delay_jiffies =
> > > msecs_to_jiffies(freezer->duty.ratio *
> > > +
> > > freezer->duty.period_pct_ms);
> > > + } else {
> > > + goal_state = CGROUP_THAWED;
> > > + delay_jiffies = msecs_to_jiffies((100 -
> > > freezer->duty.ratio) *
> > > +
> > > freezer->duty.period_pct_ms);
> > > + }
> > > + freezer_change_state(freezer->css.cgroup, goal_state);
> >
> > __freezer_change_state(freezer->css.cgroup, goal_state);
> > spin_unlock(&freezer->lock);
> >
> > (where the __freezer_change_state() function expects to already have
> > the freezer lock -- you can make that your first patch and this your
> > second)
> >
> > But you ought to double check the lock ordering, may-sleep, and
> > whether the _irq variants are correct.
> >
> I agree with the change to deal with race but again, I don't see the
> harm of the race other than delaying one period. If the user has to
> change period and duty ratio separately, there will always be a window
> of unwanted params unless user disable it first.
But those windows could be pretty large if you delay it that long and
that could be confusing. With the lock will it be delayed?
> Can you please explain the problem might be caused by the race.
> > > +
> > > +exit_toggle:
> > > + schedule_delayed_work(&freezer->freezer_work,
> > > delay_jiffies);
> > > + freezer->toggle.freeze_thaw ^= 1;
> >
> > This looks wrong. It looks like there could be a race between the next
> > scheduled work and the toggling of the freeze_thaw value. This race
> > would cause the cgroup to miss one or more duty cycles. You'd have
> > to re-order these two lines and probably need an smp barrier of one
> > sort or another between them.
> >
> I will fix that. good point.
>
>
> > Of course if you use locking and eliminate the toggle.freeze_thaw
> > field as I've suggested then you can ignore this.
> >
> same as before, not sure how to reuse the freezer spin lock for this.
> can you please explain.
Well you just need to acquire the spin lock when you enter the timer
function, calculate delay_jiffies and goal state without the need for
the freeze_thaw field, then drop the lock.
At that point you can initiate the state change and then do the
schedule_delayed_work().
<snip>
> > > @@ -360,7 +435,18 @@ static int freezer_write(struct cgroup *cgroup,
> > > goal_state = CGROUP_FROZEN;
> > > else
> > > return -EINVAL;
> > > -
> > > + /* we should stop duty ratio toggling if user wants to
> > > + * force change to a valid state.
> > > + */
> > > + freezer = cgroup_freezer(cgroup);
> > > + if (freezer->duty.period_pct_ms && freezer->duty.ratio <
> > > 100) {
> >
> > If duty.ratio is 100 then the delayed work should be cancelled too.
> > In fact it doesn't matter what the duty.ratio or period_pct_ms are --
> > writes to this file should always disable the duty cycle. Thus
> > you can omit the above if () and do this:
> >
> > > + if (freezer->toggle.enabled)
> >
> agreed, i will fix it.
> > {
> >
> > > +
> > > cancel_delayed_work_sync(&freezer->freezer_work);
> > > + freezer->duty.ratio = 0;
> >
> > Actually, shouldn't this be 0 if the cgroup is going to be thawed and
> > 100 if it's going to be frozen?
> >
> I am using 0 as an invalid value when toggle is not enabled. perhaps i
> should introduce -1 such that when user override occurs we just do
> freezer->toggle.enabled = 0;
> freezer->duty.ratio = -1;
> freezer->duty.period_pct_ms = -1;
> then we can allow and or 100% where both will turn off toggle as well.
Nope. Then you will have "negative" sleeps in the timer function which
just begs for misinterpretation. For example, look at msleep -- it takes an
unsigned int. This coupled with the race is a recipe for an unintended
long sleeps.
We don't need special values here -- just the enabled flag. When
enabled you can report the ratio from the ratio field. When not enabled
you can report the ratio by looking at the freezer state (might
want to do an update_if_frozen() first). Or you could just have writes
to the freezer.state always update the ratio. You don't need to vary
period_pct_ms at all when enabling/disabling the duty ratio.
That way at all times the values reported to userspace are consistent,
there are no "special" values, and writes to either file trigger the
correct changes between enabled/disabled and freezer state. For example
you might do:
$ echo 0 > freezer.frozen_time_pct
$ cat freezer.state
THAWED
$ cat freezer.frozen_time_pct
0
$ echo 100 > freezer.frozen_time_pct
$ cat freezer.state
FREEZING
$ cat freezer.state
FROZEN
$ cat freezer.frozen_time_pct
100
$ echo THAWED > freezer.state
$ cat freezer.frozen_time_pct
0
>
> > > + freezer->duty.period_pct_ms = 0;
> >
> > I think this should always be a non-zero value -- even when duty
> > cycling is disabled. Perhaps:
> >
> > freezer->duty.period_pct_ms = 1000/100;
> >
> > So it's clear the default period is 1000ms and one percent of it is
> > 10ms.
> >
> > (NOTE: To make it always non-zero you also need to add one line to the
> > cgroup initialization code in freezer_create()).
> how about -1 as suggested above.
>
> >
> > > + freezer->toggle.enabled = 0;
> > > + pr_info("freezer state changed by user, stop duty
> > > ratio\n");
> >
> > nit: I don't think this pr_info() is terribly useful.
> >
> I will make it pr_debug instead.
Hmm, OK I suppose.
<snip>
> > > +
> > > + switch (cft->private) {
> > > + case FREEZER_DUTY_RATIO:
> > > + if (val >= 100) {
> >
> > ratio == 100 ought to be allowed too.
> Ok, 100% frozen would be equivalent to echo FROZEN > freezer.state. I
> will document these corner cases. I think as long as these behaviors
Actually the tricky part to document has nothing to do with the
value of frozen_time_pct being 0 or 100. It has everything to do with
which write happened "last".
For all freezer.state values the value that should be read from
freezer.frozen_time_pct depends on whether it's due to a write to
freezer.frozen_time_pct or freezer.state. Writes directly to
freezer.frozen_time_pct should show what was written (if it's in 0-100
inclusive). Writes to freezer.state should appear to modify
freezer.frozen_time_pct to be consistent.
That's easily managed within the respective write functions.
Alternately, the read function for freezer.frozen_time_pct could check
the enabled bit and use that to switch which method it uses to
"read" the value.
Note how the period has nothing to do with any of this. It's just
a timescale factor which ensures there's a maximum frequency at which
we can change between FROZEN and THAWED (soon to be 1HZ).
> are documented well so that user can get the anticipated results, the
> interface does matter that much.
>
> >
> > > + ret = -EINVAL;
> > > + goto exit;
> > > + }
> >
> > Add:
> >
> > spin_lock_irq(&freezer->lock);
> >
> > > + freezer->duty.ratio = val;
> >
> > Because this can race with the delayed work.
> >
> > > + break;
> > > + case FREEZER_PERIOD:
> > > + do_div(val, 100);
> > > + freezer->duty.period_pct_ms = val;
> >
> > This can race with the delayed work. Also I think that a 0ms
> > period_pct_ms should be disallowed. Otherwise all the work delays go
> > to zero and we'll probably peg the CPU so that it's just spinning the
> > freezer state between FROZEN and THAWED and doing nothing else.
> >
> 0 or low number of period is dangerous for reason as you mentioned,
> I think I should move back to one second resolution. Especially, we are
> using common workqueue now.
Sounds good.
<snip>
> > > + /* only use delayed work when valid params are given. */
> > > + if (freezer->duty.ratio && freezer->duty.period_pct_ms &&
> > > + !freezer->toggle.enabled) {
> > > + pr_debug("starting duty ratio mode\n");
> > > + INIT_DELAYED_WORK(&freezer->freezer_work,
> > > freezer_work_fn);
> > > + freezer->toggle.enabled = 1;
> > > + schedule_delayed_work(&freezer->freezer_work, 0);
> > > + } else if ((!freezer->duty.ratio
> > > || !freezer->duty.period_pct_ms) &&
> > > + freezer->toggle.enabled) {
> > > + pr_debug("invalid param, stop duty ratio mode
> > > %p\n",
> > > + freezer->freezer_work.work.func);
> > > + cancel_delayed_work_sync(&freezer->freezer_work);
> > > + freezer->toggle.enabled = 0;
> > > + /* thaw the cgroup if we are not toggling */
> > > + freezer_change_state(freezer->css.cgroup,
> > > CGROUP_THAWED); +
> > > + }
> >
> > I don't think this is as readable as (assuming the change above to
> > disallow setting period_pct_ms to 0):
> >
> > if (freezer->duty.ratio == 100) {
> > freezer_disable_duty_cycling(freezer); /* see helper
> > below */ __freezer_change_state(freezer->css.cgroup, CGROUP_FROZEN);
> > } else if (freezer->duty.ratio == 0) {
> > freezer_disable_duty_cycling(freezer);
> > __freezer_change_state(freezer->css.cgroup,
> > CGROUP_THAWED); } else {
> > if (freezer->toggle.enabled)
> > goto exit; /* Already enabled */
> > INIT_DELAYED_WORK(&freezer->freezer_work,
> > freezer_work_fn); freezer->toggle.enabled = 1;
> > schedule_delayed_work(&freezer->freezer_work, 0);
> > }
> > spin_unlock_irq(&freezer->lock);
Something to look into: you might even be able to factor this chunk to
share it between both cgroup file write functions.
Cheers,
-Matt Helsley
On Sun, 13 Feb 2011 19:23:10 -0800
Arjan van de Ven <[email protected]> wrote:
> On 2/13/2011 4:44 PM, KAMEZAWA Hiroyuki wrote:
> > On Sat, 12 Feb 2011 15:29:07 -0800
> > Matt Helsley<[email protected]> wrote:
> >
> >> On Fri, Feb 11, 2011 at 11:10:44AM -0800, [email protected] wrote:
> >>> From: Jacob Pan<[email protected]>
> >>>
> >>> Freezer subsystem is used to manage batch jobs which can start
> >>> stop at the same time. However, sometime it is desirable to let
> >>> the kernel manage the freezer state automatically with a given
> >>> duty ratio.
> >>> For example, if we want to reduce the time that backgroup apps
> >>> are allowed to run we can put them into a freezer subsystem and
> >>> set the kernel to turn them THAWED/FROZEN at given duty ratio.
> >>>
> >>> This patch introduces two file nodes under cgroup
> >>> freezer.duty_ratio_pct and freezer.period_sec
> >> Again: I don't think this is the right approach in the long term.
> >> It would be better not to add this interface and instead enable the
> >> cpu cgroup subsystem for non-rt tasks using a similar duty ratio
> >> concept..
> >>
> >> Nevertheless, I've added some feedback on the code for you here :).
> >>
> > AFAIK, there was a work for bandwidth control in CFS.
> >
> > http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-10/msg04335.html
> >
> > I tested this and worked fine. This schduler approach seems better for
> > my purpose to limit bandwidth of apprications rather than freezer.
>
> for our purpose, it's not about bandwidth.
> it's about making sure the class of apps don't run for a long period
> (30-second range) of time.
>
The discussion about this patchset seems to have been upside-down: lots
of talk about a particular implementation, with people walking back
from the implemetnation trying to work out what the requirements were,
then seeing if other implementations might suit those requirements.
Whatever they were.
I think it would be helpful to start again, ignoring (for now) any
implementation.
What are the requirements here, guys? What effects are we actually
trying to achieve? Once that is understood and agreed to, we can
think about implementations.
And maybe you people _are_ clear about the requirements. But I'm not and
I'm sure many others aren't too. A clear statement of them would help
things along and would doubtless lead to better code. This is pretty
basic stuff!
On Mon, 14 Feb 2011 15:07:30 -0800
Andrew Morton <[email protected]> wrote:
> On Sun, 13 Feb 2011 19:23:10 -0800
> Arjan van de Ven <[email protected]> wrote:
>
> > On 2/13/2011 4:44 PM, KAMEZAWA Hiroyuki wrote:
> > > On Sat, 12 Feb 2011 15:29:07 -0800
> > > Matt Helsley<[email protected]> wrote:
> > >
> > >> On Fri, Feb 11, 2011 at 11:10:44AM -0800, [email protected] wrote:
> > >>> From: Jacob Pan<[email protected]>
> > >>>
> > >>> Freezer subsystem is used to manage batch jobs which can start
> > >>> stop at the same time. However, sometime it is desirable to let
> > >>> the kernel manage the freezer state automatically with a given
> > >>> duty ratio.
> > >>> For example, if we want to reduce the time that backgroup apps
> > >>> are allowed to run we can put them into a freezer subsystem and
> > >>> set the kernel to turn them THAWED/FROZEN at given duty ratio.
> > >>>
> > >>> This patch introduces two file nodes under cgroup
> > >>> freezer.duty_ratio_pct and freezer.period_sec
> > >> Again: I don't think this is the right approach in the long term.
> > >> It would be better not to add this interface and instead enable the
> > >> cpu cgroup subsystem for non-rt tasks using a similar duty ratio
> > >> concept..
> > >>
> > >> Nevertheless, I've added some feedback on the code for you here :).
> > >>
> > > AFAIK, there was a work for bandwidth control in CFS.
> > >
> > > http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-10/msg04335.html
> > >
> > > I tested this and worked fine. This schduler approach seems better for
> > > my purpose to limit bandwidth of apprications rather than freezer.
> >
> > for our purpose, it's not about bandwidth.
> > it's about making sure the class of apps don't run for a long period
> > (30-second range) of time.
> >
>
> The discussion about this patchset seems to have been upside-down: lots
> of talk about a particular implementation, with people walking back
> from the implemetnation trying to work out what the requirements were,
> then seeing if other implementations might suit those requirements.
> Whatever they were.
>
> I think it would be helpful to start again, ignoring (for now) any
> implementation.
>
>
> What are the requirements here, guys? What effects are we actually
> trying to achieve? Once that is understood and agreed to, we can
> think about implementations.
>
>
> And maybe you people _are_ clear about the requirements. But I'm not and
> I'm sure many others aren't too. A clear statement of them would help
> things along and would doubtless lead to better code. This is pretty
> basic stuff!
>
Ok, my(our) reuquirement is mostly 2 requirements.
- control batch jobs.
- control kvm and limit usage of cpu.
Considering kvm, we need to allow putting intaractive jobs and
batch jobs onto a cpu. This will be difference in requirements.
We need some latency sensitive control and static guarantee in peformance
limit. For example, when a user limits a process to use 50% of cpu.
Checks cpu usage by 'top -d 1', and should see almost '50%' value.
IIUC, freezer is like a system to deliver SIGSTOP. set tasks as
TASK_UNINTERRUPTIBLE and make them sleep. This check is done at
places usual signal-check and some hooks in kernel threads.
This means the subsystem checks all threads one by one and set flags,
make them TASK_UNINTERRUPTIBLE finally when them wakes up.
So, sleep/wakeup cost depeneds on the number of tasks and a task may
not be freezable until it finds hooks of try_to_freeze().
I hear when using FUSE, a task may never freeze if a process for FUSE operation
is freezed before it freezes. This sounds freezer cgroup is not easy to use.
CFS+bandwidh is a scheduler.
It removes a sub scheduler entity from a tree when it exceeds allowed time
slice. The cost of calculation of allowed time slice is involved in scheduler
but I think it will not be too heavy. (Because MAINTAINERS will see what's
going on and they are sensitive to the cost.)
Tasks are all RUNNABLE. A task in group releases cpu when it see
'reschedule' flag. We have plenty of hooks of cond_resched(). (And we know
we tries to change spin_lock to mutex if spin_lock is huge cost)
This will show a good result of perofmance even with 'top -d 1'. We'll not see
TASK_RUNNING <-> TASK_INTERRUPTIBLE status change. And I think
we can make period of time slice smaller than using freezer for better latency.
Thanks,
-Kame
On Mon, 14 Feb 2011 15:09:33 -0800
Matt Helsley <[email protected]> wrote:
> On Mon, Feb 14, 2011 at 11:41:42AM -0800, jacob pan wrote:
> > On Sat, 12 Feb 2011 15:29:07 -0800
> > Matt Helsley <[email protected]> wrote:
> >
> > > On Fri, Feb 11, 2011 at 11:10:44AM -0800,
> > > [email protected] wrote:
> > > > From: Jacob Pan <[email protected]>
>
> <snip>
>
> > > > cgroup. +To make the tasks frozen at 90% of the time every 5
> > > > seconds, do: +
> > > > +[root@localhost ]# echo 90 > freezer.duty_ratio_pct
> > > > +[root@localhost ]# echo 5000 > freezer.period_ms
> > > > +
> > > > +After that, the application in this freezer cgroup will only be
> > > > +allowed to run at the following pattern.
> > > > + __ __ __
> > > > + | |<-- 90% frozen -->| | | |
> > > > +____| |__________________| |__________________| |_____
> > > > +
> > > > + |<---- 5 seconds ---->|
> > >
> > > So most of the time I've been reviewing this I managed to invert
> > > it! I imagined "duty" meant the tasks were "on duty" ie runnable
> > > ie thawed. But according this this documentation it's the
> > > opposite...
> > >
> > My logic is that since this is a freezer, so positive logic should
> > be frozen instead of thaw.
>
> Yup, I figured as much. That's the reason I didn't ask you to swap the
> meaning of the ratio values.
>
> > > I've reviewed my review and now my comments are consistent with
> > > the above. :) However it makes me wonder if there are better
> > > names which would avoid this confusion.
> > >
> > How about frozen_time_pct?
>
using frozen_time_percentage in v9
> Much better! nit: I don't know if _pct is obvious to everyone but it
> only takes 4 more characters to make it so..
>
> > > > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
>
> <snip>
>
> > > > +static void freezer_work_fn(struct work_struct *work)
> > > > +{
> > > > + struct freezer *freezer;
> > > > + unsigned long delay_jiffies = 0;
> > > > + enum freezer_state goal_state;
> > > > +
> > >
> > > Looking better. There are alot of field accesses here which can
> > > race with writes to the cgroup's duty ratio and period files.
> > > They should be protected. Perhaps we can reuse the freezer spin
> > > lock. That also has the benefit that we can eliminate the
> > > toggle.freeze_thaw bit I think:
> > >
> > I did think about the race, it does exist. but in practice. My
> > thought was that since freezer_change_state() holds the spin_lock
> > of the freezer, the race with writes to params are harmless, it
> > just means the new period or ratio will take effect in the next
> > period.
>
> I considered this but didn't like the idea of relying on it. More
> below.
>
fair enough, I added spin lock in v9
> > In terms of using freezer spin lock to eliminate toggle flag, I am
> > not sure if i know how to do that. Are you suggesting based on
> > whether the spin lock is taken or not, we can decide the toggle?
> > but the freeze spin lock is used by other functions as well not
> > just the delay work here. I guess I have missed something.
>
> I was thinking that with the lock held you can check the state
> variable and just do the "opposite" of what it indicates:
>
> state TODO
> FROZEN THAWED
> FREEZING THAWED
> THAWED FROZEN
>
> Then you don't need the separate bit to indicate which state it should
> try to change to next.
> ]
good idea, using it in v9
> > > > +
> > > > + freezer = container_of(work, struct freezer,
> > > > freezer_work.work);
> > > > + /* toggle between THAWED and FROZEN state.
> > > > + * thaw if freezer->toggle.freeze_thaw = 0; freeze
> > > > otherwise
> > > > + * skip the first round if already in the target
> > > > states.
> > > > + */
> > >
> > > spin_lock(&freezer->lock);
> > >
> > > > + if ((freezer->toggle.freeze_thaw && freezer->state ==
> > > > CGROUP_FROZEN) ||
> > > > + (!freezer->toggle.freeze_thaw &&
> > > > + freezer->state == CGROUP_THAWED)) {
> > > > + delay_jiffies = 0;
> > >
> > > This looks wrong. We should never schedule freezer work delayed
> > > by 0 jiffies -- even if the delayed work API allows it. With
> > > 0-length delays I'd worry that we could peg the CPU in an obscure
> > > infinite loop.
> > >
> > > I think you can safely eliminate this block and the "exit_toggle"
> > > label.
> > >
> > Good point. My initial thought was that since the period for
> > targeted usage is quite long, e.g. 30 sec., we want to start the
> > duty ratio right away. But that shouldn't matter since we already
> > schedule work based on the new ratio/period.
> > > > + goto exit_toggle;
> > > > + } else if (freezer->toggle.freeze_thaw) {
> > >
> > > if (freezer->state == CGROUP_THAWED) {
> > >
> > > > + goal_state = CGROUP_FROZEN;
> > > > + delay_jiffies =
> > > > msecs_to_jiffies(freezer->duty.ratio *
> > > > +
> > > > freezer->duty.period_pct_ms);
> > > > + } else {
> > > > + goal_state = CGROUP_THAWED;
> > > > + delay_jiffies = msecs_to_jiffies((100 -
> > > > freezer->duty.ratio) *
> > > > +
> > > > freezer->duty.period_pct_ms);
> > > > + }
> > > > + freezer_change_state(freezer->css.cgroup, goal_state);
> > >
> > > __freezer_change_state(freezer->css.cgroup, goal_state);
> > > spin_unlock(&freezer->lock);
> > >
> > > (where the __freezer_change_state() function expects to already
> > > have the freezer lock -- you can make that your first patch and
> > > this your second)
> > >
> > > But you ought to double check the lock ordering, may-sleep, and
> > > whether the _irq variants are correct.
> > >
> > I agree with the change to deal with race but again, I don't see the
> > harm of the race other than delaying one period. If the user has to
> > change period and duty ratio separately, there will always be a
> > window of unwanted params unless user disable it first.
>
> But those windows could be pretty large if you delay it that long and
> that could be confusing. With the lock will it be delayed?
>
There is no way to prevent such window. e.g. if user wants to change
from 50% of 3 second period to 90% of 2 second period, it will get a
mismatch for one period. lock does not help here. Users just have to
disable the toggling mode if they want to prevent that.
> > Can you please explain the problem might be caused by the race.
> > > > +
> > > > +exit_toggle:
> > > > + schedule_delayed_work(&freezer->freezer_work,
> > > > delay_jiffies);
> > > > + freezer->toggle.freeze_thaw ^= 1;
> > >
> > > This looks wrong. It looks like there could be a race between the
> > > next scheduled work and the toggling of the freeze_thaw value.
> > > This race would cause the cgroup to miss one or more duty cycles.
> > > You'd have to re-order these two lines and probably need an smp
> > > barrier of one sort or another between them.
> > >
> > I will fix that. good point.
> >
> >
> > > Of course if you use locking and eliminate the toggle.freeze_thaw
> > > field as I've suggested then you can ignore this.
> > >
> > same as before, not sure how to reuse the freezer spin lock for
> > this. can you please explain.
>
> Well you just need to acquire the spin lock when you enter the timer
> function, calculate delay_jiffies and goal state without the need for
> the freeze_thaw field, then drop the lock.
>
> At that point you can initiate the state change and then do the
> schedule_delayed_work().
>
> <snip>
done in v9.
>
> > > > @@ -360,7 +435,18 @@ static int freezer_write(struct cgroup
> > > > *cgroup, goal_state = CGROUP_FROZEN;
> > > > else
> > > > return -EINVAL;
> > > > -
> > > > + /* we should stop duty ratio toggling if user wants to
> > > > + * force change to a valid state.
> > > > + */
> > > > + freezer = cgroup_freezer(cgroup);
> > > > + if (freezer->duty.period_pct_ms && freezer->duty.ratio
> > > > < 100) {
> > >
> > > If duty.ratio is 100 then the delayed work should be cancelled
> > > too. In fact it doesn't matter what the duty.ratio or
> > > period_pct_ms are -- writes to this file should always disable
> > > the duty cycle. Thus you can omit the above if () and do this:
> > >
> > > > + if (freezer->toggle.enabled)
> > >
> > agreed, i will fix it.
> > > {
> > >
> > > > +
> > > > cancel_delayed_work_sync(&freezer->freezer_work);
> > > > + freezer->duty.ratio = 0;
> > >
> > > Actually, shouldn't this be 0 if the cgroup is going to be thawed
> > > and 100 if it's going to be frozen?
> > >
> > I am using 0 as an invalid value when toggle is not enabled.
> > perhaps i should introduce -1 such that when user override occurs
> > we just do freezer->toggle.enabled = 0;
> > freezer->duty.ratio = -1;
> > freezer->duty.period_pct_ms = -1;
> > then we can allow and or 100% where both will turn off toggle as
> > well.
>
> Nope. Then you will have "negative" sleeps in the timer function which
> just begs for misinterpretation. For example, look at msleep -- it
> takes an unsigned int. This coupled with the race is a recipe for an
> unintended long sleeps.
>
> We don't need special values here -- just the enabled flag. When
> enabled you can report the ratio from the ratio field. When not
> enabled you can report the ratio by looking at the freezer state
> (might want to do an update_if_frozen() first). Or you could just
> have writes to the freezer.state always update the ratio. You don't
> need to vary period_pct_ms at all when enabling/disabling the duty
> ratio.
>
> That way at all times the values reported to userspace are consistent,
> there are no "special" values, and writes to either file trigger the
> correct changes between enabled/disabled and freezer state. For
> example you might do:
>
> $ echo 0 > freezer.frozen_time_pct
> $ cat freezer.state
> THAWED
> $ cat freezer.frozen_time_pct
> 0
> $ echo 100 > freezer.frozen_time_pct
> $ cat freezer.state
> FREEZING
> $ cat freezer.state
> FROZEN
> $ cat freezer.frozen_time_pct
> 100
> $ echo THAWED > freezer.state
> $ cat freezer.frozen_time_pct
> 0
>
fixed in v9
> >
> > > > + freezer->duty.period_pct_ms = 0;
> > >
> > > I think this should always be a non-zero value -- even when duty
> > > cycling is disabled. Perhaps:
> > >
> > > freezer->duty.period_pct_ms = 1000/100;
> > >
> > > So it's clear the default period is 1000ms and one percent of it
> > > is 10ms.
> > >
> > > (NOTE: To make it always non-zero you also need to add one line
> > > to the cgroup initialization code in freezer_create()).
> > how about -1 as suggested above.
> >
> > >
> > > > + freezer->toggle.enabled = 0;
> > > > + pr_info("freezer state changed by user, stop
> > > > duty ratio\n");
> > >
> > > nit: I don't think this pr_info() is terribly useful.
> > >
> > I will make it pr_debug instead.
>
> Hmm, OK I suppose.
>
> <snip>
>
> > > > +
> > > > + switch (cft->private) {
> > > > + case FREEZER_DUTY_RATIO:
> > > > + if (val >= 100) {
> > >
> > > ratio == 100 ought to be allowed too.
> > Ok, 100% frozen would be equivalent to echo FROZEN > freezer.state.
> > I will document these corner cases. I think as long as these
> > behaviors
>
> Actually the tricky part to document has nothing to do with the
> value of frozen_time_pct being 0 or 100. It has everything to do with
> which write happened "last".
>
> For all freezer.state values the value that should be read from
> freezer.frozen_time_pct depends on whether it's due to a write to
> freezer.frozen_time_pct or freezer.state. Writes directly to
> freezer.frozen_time_pct should show what was written (if it's in 0-100
> inclusive). Writes to freezer.state should appear to modify
> freezer.frozen_time_pct to be consistent.
>
> That's easily managed within the respective write functions.
> Alternately, the read function for freezer.frozen_time_pct could check
> the enabled bit and use that to switch which method it uses to
> "read" the value.
>
> Note how the period has nothing to do with any of this. It's just
> a timescale factor which ensures there's a maximum frequency at which
> we can change between FROZEN and THAWED (soon to be 1HZ).
>
little confused, there is no need to "appear to modify" things. I just
made freezer.state write in sync with ratio value.
> > are documented well so that user can get the anticipated results,
> > the interface does matter that much.
> >
> > >
> > > > + ret = -EINVAL;
> > > > + goto exit;
> > > > + }
> > >
> > > Add:
> > >
> > > spin_lock_irq(&freezer->lock);
> > >
> > > > + freezer->duty.ratio = val;
> > >
> > > Because this can race with the delayed work.
> > >
> > > > + break;
> > > > + case FREEZER_PERIOD:
> > > > + do_div(val, 100);
> > > > + freezer->duty.period_pct_ms = val;
> > >
> > > This can race with the delayed work. Also I think that a 0ms
> > > period_pct_ms should be disallowed. Otherwise all the work delays
> > > go to zero and we'll probably peg the CPU so that it's just
> > > spinning the freezer state between FROZEN and THAWED and doing
> > > nothing else.
> > >
> > 0 or low number of period is dangerous for reason as you mentioned,
> > I think I should move back to one second resolution. Especially, we
> > are using common workqueue now.
>
> Sounds good.
>
> <snip>
>
> > > > + /* only use delayed work when valid params are given.
> > > > */
> > > > + if (freezer->duty.ratio && freezer->duty.period_pct_ms
> > > > &&
> > > > + !freezer->toggle.enabled) {
> > > > + pr_debug("starting duty ratio mode\n");
> > > > + INIT_DELAYED_WORK(&freezer->freezer_work,
> > > > freezer_work_fn);
> > > > + freezer->toggle.enabled = 1;
> > > > + schedule_delayed_work(&freezer->freezer_work,
> > > > 0);
> > > > + } else if ((!freezer->duty.ratio
> > > > || !freezer->duty.period_pct_ms) &&
> > > > + freezer->toggle.enabled) {
> > > > + pr_debug("invalid param, stop duty ratio mode
> > > > %p\n",
> > > > + freezer->freezer_work.work.func);
> > > > +
> > > > cancel_delayed_work_sync(&freezer->freezer_work);
> > > > + freezer->toggle.enabled = 0;
> > > > + /* thaw the cgroup if we are not toggling */
> > > > + freezer_change_state(freezer->css.cgroup,
> > > > CGROUP_THAWED); +
> > > > + }
> > >
> > > I don't think this is as readable as (assuming the change above to
> > > disallow setting period_pct_ms to 0):
> > >
> > > if (freezer->duty.ratio == 100) {
> > > freezer_disable_duty_cycling(freezer); /* see
> > > helper below */ __freezer_change_state(freezer->css.cgroup,
> > > CGROUP_FROZEN); } else if (freezer->duty.ratio == 0) {
> > > freezer_disable_duty_cycling(freezer);
> > > __freezer_change_state(freezer->css.cgroup,
> > > CGROUP_THAWED); } else {
> > > if (freezer->toggle.enabled)
> > > goto exit; /* Already enabled */
> > > INIT_DELAYED_WORK(&freezer->freezer_work,
> > > freezer_work_fn); freezer->toggle.enabled = 1;
> > > schedule_delayed_work(&freezer->freezer_work, 0);
> > > }
> > > spin_unlock_irq(&freezer->lock);
>
> Something to look into: you might even be able to factor this chunk to
> share it between both cgroup file write functions.
>
I did some consolidation in v9, the checks for cancellation are all
merged in one function now.
I did not introduce __freezer_change_state() but rather just use the
internal freeze and unfreeze function w/o lock (when caller already has
the lock).
Thanks,
Jacob
On Tue, 15 Feb 2011 11:18:57 +0900
KAMEZAWA Hiroyuki <[email protected]> wrote:
> On Mon, 14 Feb 2011 15:07:30 -0800
> Andrew Morton <[email protected]> wrote:
>
> > On Sun, 13 Feb 2011 19:23:10 -0800
> > Arjan van de Ven <[email protected]> wrote:
> >
> > > On 2/13/2011 4:44 PM, KAMEZAWA Hiroyuki wrote:
> > > > On Sat, 12 Feb 2011 15:29:07 -0800
> > > > Matt Helsley<[email protected]> wrote:
> > > >
> > > >> On Fri, Feb 11, 2011 at 11:10:44AM -0800,
> > > >> [email protected] wrote:
> > > >>> From: Jacob Pan<[email protected]>
> > > >>>
> > > >>> Freezer subsystem is used to manage batch jobs which can start
> > > >>> stop at the same time. However, sometime it is desirable to
> > > >>> let the kernel manage the freezer state automatically with a
> > > >>> given duty ratio.
> > > >>> For example, if we want to reduce the time that backgroup apps
> > > >>> are allowed to run we can put them into a freezer subsystem
> > > >>> and set the kernel to turn them THAWED/FROZEN at given duty
> > > >>> ratio.
> > > >>>
> > > >>> This patch introduces two file nodes under cgroup
> > > >>> freezer.duty_ratio_pct and freezer.period_sec
> > > >> Again: I don't think this is the right approach in the long
> > > >> term. It would be better not to add this interface and instead
> > > >> enable the cpu cgroup subsystem for non-rt tasks using a
> > > >> similar duty ratio concept..
> > > >>
> > > >> Nevertheless, I've added some feedback on the code for you
> > > >> here :).
> > > >>
> > > > AFAIK, there was a work for bandwidth control in CFS.
> > > >
> > > > http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-10/msg04335.html
> > > >
> > > > I tested this and worked fine. This schduler approach seems
> > > > better for my purpose to limit bandwidth of apprications rather
> > > > than freezer.
> > >
> > > for our purpose, it's not about bandwidth.
> > > it's about making sure the class of apps don't run for a long
> > > period (30-second range) of time.
> > >
> >
> > The discussion about this patchset seems to have been upside-down:
> > lots of talk about a particular implementation, with people walking
> > back from the implemetnation trying to work out what the
> > requirements were, then seeing if other implementations might suit
> > those requirements. Whatever they were.
> >
> > I think it would be helpful to start again, ignoring (for now) any
> > implementation.
> >
> >
> > What are the requirements here, guys? What effects are we actually
> > trying to achieve? Once that is understood and agreed to, we can
> > think about implementations.
> >
> >
> > And maybe you people _are_ clear about the requirements. But I'm
> > not and I'm sure many others aren't too. A clear statement of them
> > would help things along and would doubtless lead to better code.
> > This is pretty basic stuff!
> >
>
> Ok, my(our) reuquirement is mostly 2 requirements.
>
> - control batch jobs.
> - control kvm and limit usage of cpu.
>
> Considering kvm, we need to allow putting intaractive jobs and
> batch jobs onto a cpu. This will be difference in requirements.
> We need some latency sensitive control and static guarantee in
> peformance limit. For example, when a user limits a process to use
> 50% of cpu. Checks cpu usage by 'top -d 1', and should see almost
> '50%' value.
>
>
> IIUC, freezer is like a system to deliver SIGSTOP. set tasks as
> TASK_UNINTERRUPTIBLE and make them sleep. This check is done at
> places usual signal-check and some hooks in kernel threads.
> This means the subsystem checks all threads one by one and set flags,
> make them TASK_UNINTERRUPTIBLE finally when them wakes up.
> So, sleep/wakeup cost depeneds on the number of tasks and a task may
> not be freezable until it finds hooks of try_to_freeze().
>
> I hear when using FUSE, a task may never freeze if a process for FUSE
> operation is freezed before it freezes. This sounds freezer cgroup is
> not easy to use.
>
> CFS+bandwidh is a scheduler.
> It removes a sub scheduler entity from a tree when it exceeds allowed
> time slice. The cost of calculation of allowed time slice is involved
> in scheduler but I think it will not be too heavy. (Because
> MAINTAINERS will see what's going on and they are sensitive to the
> cost.) Tasks are all RUNNABLE. A task in group releases cpu when it
> see 'reschedule' flag. We have plenty of hooks of cond_resched().
> (And we know we tries to change spin_lock to mutex if spin_lock is
> huge cost)
>
> This will show a good result of perofmance even with 'top -d 1'.
> We'll not see TASK_RUNNING <-> TASK_INTERRUPTIBLE status change. And
> I think we can make period of time slice smaller than using freezer
> for better latency.
>
Thanks for the info. I will give it a try in my setup and get back to
you all.