Allow sysctl override of sched_tick_max_deferment in order to ease
finding/fixing the remaining issues with full nohz.
The value to be written is in jiffies, and -1 means the max deferment
is disabled (scheduler_tick_max_deferment() returns KTIME_MAX.)
Cc: Frederic Weisbecker <[email protected]>
Signed-off-by: Kevin Hilman <[email protected]>
---
include/linux/sched/sysctl.h | 3 +++
kernel/sched/core.c | 6 +++++-
kernel/sched/debug.c | 1 +
kernel/sysctl.c | 9 +++++++++
4 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index bf8086b..2ad07bb 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -57,6 +57,9 @@ extern unsigned int sysctl_sched_nr_migrate;
extern unsigned int sysctl_sched_time_avg;
extern unsigned int sysctl_timer_migration;
extern unsigned int sysctl_sched_shares_window;
+#ifdef CONFIG_NO_HZ_FULL
+extern unsigned int sysctl_sched_tick_max_deferment;
+#endif
int sched_proc_update_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *length,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e1a27f9..b5d3f99 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2751,12 +2751,16 @@ void scheduler_tick(void)
* balancing, etc... continue to move forward, even
* with a very low granularity.
*/
+unsigned int sysctl_sched_tick_max_deferment = HZ;
u64 scheduler_tick_max_deferment(void)
{
struct rq *rq = this_rq();
unsigned long next, now = ACCESS_ONCE(jiffies);
- next = rq->last_sched_tick + HZ;
+ if (sysctl_sched_tick_max_deferment == -1)
+ return KTIME_MAX;
+
+ next = rq->last_sched_tick + sysctl_sched_tick_max_deferment;
if (time_before_eq(next, now))
return 0;
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 75024a6..f445ab9 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -374,6 +374,7 @@ static void sched_debug_header(struct seq_file *m)
PN(sysctl_sched_wakeup_granularity);
P(sysctl_sched_child_runs_first);
P(sysctl_sched_features);
+ P(sysctl_sched_tick_max_deferment);
#undef PN
#undef P
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 9edcf45..fb0b7d8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -393,6 +393,15 @@ static struct ctl_table kern_table[] = {
.proc_handler = proc_dointvec,
},
#endif /* CONFIG_NUMA_BALANCING */
+#ifdef CONFIG_NO_HZ_FULL
+ {
+ .procname = "sched_tick_max_deferment",
+ .data = &sysctl_sched_tick_max_deferment,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+#endif /* CONFIG_NO_HZ_FULL */
#endif /* CONFIG_SCHED_DEBUG */
{
.procname = "sched_rt_period_us",
--
1.8.3
The conversion of the max deferment from usecs to nsecs can easily
overflow on platforms where a long is 32-bits. To fix, cast the usecs
value to u64 before multiplying by NSECS_PER_USEC.
This was discovered on 32-bit ARM platform when extending the max
deferment value.
Cc: Frederic Weisbecker <[email protected]>
Signed-off-by: Kevin Hilman <[email protected]>
---
kernel/sched/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b5d3f99..b506722 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2765,7 +2765,7 @@ u64 scheduler_tick_max_deferment(void)
if (time_before_eq(next, now))
return 0;
- return jiffies_to_usecs(next - now) * NSEC_PER_USEC;
+ return (u64)jiffies_to_usecs(next - now) * NSEC_PER_USEC;
}
#endif
--
1.8.3
On Tue, Jun 18, 2013 at 04:58:28PM -0700, Kevin Hilman wrote:
> Allow sysctl override of sched_tick_max_deferment in order to ease
> finding/fixing the remaining issues with full nohz.
>
> The value to be written is in jiffies, and -1 means the max deferment
> is disabled (scheduler_tick_max_deferment() returns KTIME_MAX.)
>
> Cc: Frederic Weisbecker <[email protected]>
> Signed-off-by: Kevin Hilman <[email protected]>
This looks like a useful thing but I wonder if a debugfs file would
be more appropriate than sysctl.
The scheduler tick max deferment is supposed to be a temporary
hack so we probably don't want to bring a real user ABI for that.
I believe sysctl is for permanent ABIs, right?
On Tue, Jun 18, 2013 at 04:58:29PM -0700, Kevin Hilman wrote:
> The conversion of the max deferment from usecs to nsecs can easily
> overflow on platforms where a long is 32-bits. To fix, cast the usecs
> value to u64 before multiplying by NSECS_PER_USEC.
>
> This was discovered on 32-bit ARM platform when extending the max
> deferment value.
>
> Cc: Frederic Weisbecker <[email protected]>
> Signed-off-by: Kevin Hilman <[email protected]>
Right, if we make it tunable we need that patch.
Thanks!
Acked-by: Frederic Weisbecker <[email protected]>
> ---
> kernel/sched/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b5d3f99..b506722 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2765,7 +2765,7 @@ u64 scheduler_tick_max_deferment(void)
> if (time_before_eq(next, now))
> return 0;
>
> - return jiffies_to_usecs(next - now) * NSEC_PER_USEC;
> + return (u64)jiffies_to_usecs(next - now) * NSEC_PER_USEC;
> }
> #endif
>
> --
> 1.8.3
>
Frederic Weisbecker <[email protected]> writes:
> On Tue, Jun 18, 2013 at 04:58:28PM -0700, Kevin Hilman wrote:
>> Allow sysctl override of sched_tick_max_deferment in order to ease
>> finding/fixing the remaining issues with full nohz.
>>
>> The value to be written is in jiffies, and -1 means the max deferment
>> is disabled (scheduler_tick_max_deferment() returns KTIME_MAX.)
>>
>> Cc: Frederic Weisbecker <[email protected]>
>> Signed-off-by: Kevin Hilman <[email protected]>
>
> This looks like a useful thing but I wonder if a debugfs file would
> be more appropriate than sysctl.
>
> The scheduler tick max deferment is supposed to be a temporary
> hack so we probably don't want to bring a real user ABI for that.
I wondered about that as well, but I wasn't sure if the existing knobs
under CONFIG_SCHED_DEBUG (sched_min_granularity_ns, sched_latency_ns,
etc.) are considered permanant ABI, or optional debugging tools.
This new option is inside CONFIG_SCHED_DEBUG along with the others, but
if debugfs is preferred I can move it there. It seems strange though to
just have this knob in debugfs and the rest in sysctl under
CONFIG_SCHED_DEBUG.
Thanks,
Kevin