The interactivity estimator special cases tasks that are waking up from
uninterruptible sleep based on the fact that most uninterruptible sleep
represents a task waiting on disk I/O and is not truly interactive. The
current system uses a ceiling to the priority bonus said tasks can receive.
The problem with that system is that if there are enough interactive tasks
at high bonus levels it can lead to I/O starvation.
In order to remove the ceiling but still maintain some special case treatment
of uninterruptible sleep, we can make any sleep_avg incrementing to be purely
based on sleep time instead of being biased in the non-linear fashion that
interactive tasks are.
This will lead to a detriment in interactive behaviour under disk I/O however
the current system unfairly biases against them and leads to a loss of disk
throughput. This change should restore a better balance between disk
throughput and interactivity.
Signed-off-by: Con Kolivas <[email protected]>
kernel/sched.c | 36 ++++++++++++------------------------
1 files changed, 12 insertions(+), 24 deletions(-)
Index: linux-2.6.15/kernel/sched.c
===================================================================
--- linux-2.6.15.orig/kernel/sched.c
+++ linux-2.6.15/kernel/sched.c
@@ -756,26 +756,17 @@ static int recalc_task_prio(task_t *p, u
p->sleep_avg = JIFFIES_TO_NS(MAX_SLEEP_AVG -
DEF_TIMESLICE);
} else {
- /*
- * The lower the sleep avg a task has the more
- * rapidly it will rise with sleep time.
- */
- sleep_time *= (MAX_BONUS - CURRENT_BONUS(p)) ? : 1;
/*
- * Tasks waking from uninterruptible sleep are
- * limited in their sleep_avg rise as they
- * are likely to be waiting on I/O
+ * The lower the sleep avg a task has the more
+ * rapidly it will rise with sleep time. This enables
+ * tasks to rapidly recover to a low latency priority.
+ * If a task was sleeping with the noninteractive
+ * label do not apply this non-linear boost
*/
- if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
- if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
- sleep_time = 0;
- else if (p->sleep_avg + sleep_time >=
- INTERACTIVE_SLEEP(p)) {
- p->sleep_avg = INTERACTIVE_SLEEP(p);
- sleep_time = 0;
- }
- }
+ if (p->sleep_type != SLEEP_NONINTERACTIVE || p->mm)
+ sleep_time *=
+ (MAX_BONUS - CURRENT_BONUS(p)) ? : 1;
/*
* This code gives a bonus to interactive tasks.
@@ -818,11 +809,7 @@ static void activate_task(task_t *p, run
if (!rt_task(p))
p->prio = recalc_task_prio(p, now);
- /*
- * This checks to make sure it's not an uninterruptible task
- * that is now waking up.
- */
- if (p->sleep_type == SLEEP_NORMAL) {
+ if (p->sleep_type != SLEEP_NONINTERACTIVE) {
/*
* Tasks which were woken up by interrupts (ie. hw events)
* are most likely of interactive nature. So we give them
@@ -1356,8 +1343,9 @@ out_activate:
if (old_state == TASK_UNINTERRUPTIBLE) {
rq->nr_uninterruptible--;
/*
- * Tasks on involuntary sleep don't earn
- * sleep_avg beyond just interactive state.
+ * Tasks waking from uninterruptible sleep are likely
+ * to be sleeping involuntarily on I/O and are otherwise
+ * cpu bound so label them as noninteractive.
*/
p->sleep_type = SLEEP_NONINTERACTIVE;
}
Greetings,
At 09:23 PM 1/13/2006 +1100, Con Kolivas wrote:
>Index: linux-2.6.15/kernel/sched.c
>===================================================================
>--- linux-2.6.15.orig/kernel/sched.c
>+++ linux-2.6.15/kernel/sched.c
>@@ -756,26 +756,17 @@ static int recalc_task_prio(task_t *p, u
<snip>
>+ * If a task was sleeping with the noninteractive
>+ * label do not apply this non-linear boost
> */
>- if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
>- if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
>- sleep_time = 0;
>- else if (p->sleep_avg + sleep_time >=
>- INTERACTIVE_SLEEP(p)) {
>- p->sleep_avg = INTERACTIVE_SLEEP(p);
>- sleep_time = 0;
>- }
>- }
>+ if (p->sleep_type != SLEEP_NONINTERACTIVE || p->mm)
Typo alert. Looks like that should be ||
!p->mm. ^
-Mike
On Saturday 14 January 2006 23:56, Mike Galbraith wrote:
> Greetings,
>
> At 09:23 PM 1/13/2006 +1100, Con Kolivas wrote:
> >Index: linux-2.6.15/kernel/sched.c
> >===================================================================
> >--- linux-2.6.15.orig/kernel/sched.c
> >+++ linux-2.6.15/kernel/sched.c
> >@@ -756,26 +756,17 @@ static int recalc_task_prio(task_t *p, u
>
> <snip>
>
> >+ * If a task was sleeping with the noninteractive
> >+ * label do not apply this non-linear boost
> > */
> >- if (p->sleep_type == SLEEP_NONINTERACTIVE &&
> > p->mm) { - if (p->sleep_avg >=
> > INTERACTIVE_SLEEP(p)) - sleep_time
> > = 0;
> >- else if (p->sleep_avg + sleep_time >=
> >- INTERACTIVE_SLEEP(p)) {
> >- p->sleep_avg =
> > INTERACTIVE_SLEEP(p); - sleep_time
> > = 0;
> >- }
> >- }
> >+ if (p->sleep_type != SLEEP_NONINTERACTIVE ||
> > p->mm)
>
> Typo alert. Looks like that should be ||
> !p->mm. ^
Good catch!
That would have hurt like that too.
Andrew please apply to or rollup into interactivity series.
Cheers,
Con
---
Fix typo thanks Mike Galbraith for spotting.
Signed-off-by: Con Kolivas <[email protected]>
kernel/sched.c | 2 +-
1 files changed, 1 insertion(+), 1 deletion(-)
Index: linux-2.6.15/kernel/sched.c
===================================================================
--- linux-2.6.15.orig/kernel/sched.c
+++ linux-2.6.15/kernel/sched.c
@@ -768,7 +768,7 @@ static int recalc_task_prio(task_t *p, u
* If a task was sleeping with the noninteractive
* label do not apply this non-linear boost
*/
- if (p->sleep_type != SLEEP_NONINTERACTIVE || p->mm)
+ if (p->sleep_type != SLEEP_NONINTERACTIVE || !p->mm)
sleep_time *=
(MAX_BONUS - CURRENT_BONUS(p)) ? : 1;