* [PATCH] sched/rt: use for_each_cpu_wrap to iterate over rto_mask
@ 2024-11-14 22:05 Jon Kohler
2024-11-15 10:04 ` Peter Zijlstra
0 siblings, 1 reply; 2+ messages in thread
From: Jon Kohler @ 2024-11-14 22:05 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
Valentin Schneider, linux-kernel
Cc: Jon Kohler
When using NO_RT_PUSH_IPI, using for_each_cpu() over rto_mask may cause
many CPUs to attempt to pull load from the same CPU, causing RQ
lock contention.
Use for_each_cpu_wrap instead to spread out which RQ gets evaluated
first, similar to how _nohz_idle_balance iterates over idle_cpus_mask.
This strategy is beneficial when there are many CPUs in rto_mask and
many other CPUs going in and out of schedule() at the same time.
Signed-off-by: Jon Kohler <jon@nutanix.com>
---
kernel/sched/rt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 172c588de542..c883ff122f5d 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2308,7 +2308,7 @@ static void pull_rt_task(struct rq *this_rq)
}
#endif
- for_each_cpu(cpu, this_rq->rd->rto_mask) {
+ for_each_cpu_wrap(cpu, this_rq->rd->rto_mask, this_cpu+1) {
if (this_cpu == cpu)
continue;
--
2.43.0
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] sched/rt: use for_each_cpu_wrap to iterate over rto_mask
2024-11-14 22:05 [PATCH] sched/rt: use for_each_cpu_wrap to iterate over rto_mask Jon Kohler
@ 2024-11-15 10:04 ` Peter Zijlstra
0 siblings, 0 replies; 2+ messages in thread
From: Peter Zijlstra @ 2024-11-15 10:04 UTC (permalink / raw)
To: Jon Kohler
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman, Valentin Schneider,
linux-kernel
On Thu, Nov 14, 2024 at 03:05:58PM -0700, Jon Kohler wrote:
> When using NO_RT_PUSH_IPI, using for_each_cpu() over rto_mask may cause
> many CPUs to attempt to pull load from the same CPU, causing RQ
> lock contention.
>
> Use for_each_cpu_wrap instead to spread out which RQ gets evaluated
> first, similar to how _nohz_idle_balance iterates over idle_cpus_mask.
> This strategy is beneficial when there are many CPUs in rto_mask and
> many other CPUs going in and out of schedule() at the same time.
>
> Signed-off-by: Jon Kohler <jon@nutanix.com>
> ---
> kernel/sched/rt.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 172c588de542..c883ff122f5d 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2308,7 +2308,7 @@ static void pull_rt_task(struct rq *this_rq)
> }
> #endif
>
> - for_each_cpu(cpu, this_rq->rd->rto_mask) {
> + for_each_cpu_wrap(cpu, this_rq->rd->rto_mask, this_cpu+1) {
> if (this_cpu == cpu)
> continue;
Works for me I suppose, but as with that other rt patch, please do the
matching change for dl too.
^ permalink raw reply [flat|nested] 2+ messages in thread
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