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| Started by | tip-bot for Frederic Weisbecker <tipbot@zytor.com> |
|---|---|
| First post | 2017-06-22 13:20 +0200 |
| Last post | 2017-06-22 21:50 +0200 |
| Articles | 3 — 3 participants |
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[tip:sched/core] sched/fair: Spare idle load balancing on nohz_full CPUs tip-bot for Frederic Weisbecker <tipbot@zytor.com> - 2017-06-22 13:20 +0200
Re: [tip:sched/core] sched/fair: Spare idle load balancing on nohz_full CPUs Frederic Weisbecker <fweisbec@gmail.com> - 2017-06-22 16:00 +0200
Re: [tip:sched/core] sched/fair: Spare idle load balancing on nohz_full CPUs Ingo Molnar <mingo@kernel.org> - 2017-06-22 21:50 +0200
| From | tip-bot for Frederic Weisbecker <tipbot@zytor.com> |
|---|---|
| Date | 2017-06-22 13:20 +0200 |
| Subject | [tip:sched/core] sched/fair: Spare idle load balancing on nohz_full CPUs |
| Message-ID | <tV8jv-3Vn-5@gated-at.bofh.it> |
Commit-ID: 387bc8b5536eeb0a92f4b4ab553539eaea2ac0ba Gitweb: http://git.kernel.org/tip/387bc8b5536eeb0a92f4b4ab553539eaea2ac0ba Author: Frederic Weisbecker <fweisbec@gmail.com> AuthorDate: Mon, 19 Jun 2017 04:12:02 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Thu, 22 Jun 2017 11:30:02 +0200 sched/fair: Spare idle load balancing on nohz_full CPUs Although idle load balancing obviously only concerns idle CPUs, it can be a disturbance on a busy nohz_full CPU. Indeed a CPU can only get rid of an idle load balancing duty once a tick fires while it runs a task and this can take a while on a nohz_full CPU. We could fix that and escape the idle load balancing duty from the very idle exit path but that would bring unecessary overhead. Lets just not bother and leave that job to housekeeping CPUs (those outside nohz_full range). The nohz_full CPUs simply don't want any disturbance. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1497838322-10913-4-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a24661a..694c258 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8683,6 +8683,10 @@ void nohz_balance_enter_idle(int cpu) if (!cpu_active(cpu)) return; + /* Spare idle load balancing on CPUs that don't want to be disturbed: */ + if (!is_housekeeping_cpu(cpu)) + return; + if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu))) return;
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| From | Frederic Weisbecker <fweisbec@gmail.com> |
|---|---|
| Date | 2017-06-22 16:00 +0200 |
| Subject | Re: [tip:sched/core] sched/fair: Spare idle load balancing on nohz_full CPUs |
| Message-ID | <tVaOm-5tA-13@gated-at.bofh.it> |
| In reply to | #1672541 |
Hi Ingo, On Thu, Jun 22, 2017 at 04:11:53AM -0700, tip-bot for Frederic Weisbecker wrote: > Commit-ID: 387bc8b5536eeb0a92f4b4ab553539eaea2ac0ba > Gitweb: http://git.kernel.org/tip/387bc8b5536eeb0a92f4b4ab553539eaea2ac0ba > Author: Frederic Weisbecker <fweisbec@gmail.com> > AuthorDate: Mon, 19 Jun 2017 04:12:02 +0200 > Committer: Ingo Molnar <mingo@kernel.org> > CommitDate: Thu, 22 Jun 2017 11:30:02 +0200 > > sched/fair: Spare idle load balancing on nohz_full CPUs Thanks for applying the series! The two other patches are indeed good but Rik and Mike have mitigated feelings about this very patch. I think we need to decouple housekeeping from nohz_full before applying it. Is it possible to set it aside for now? Thanks!
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| From | Ingo Molnar <mingo@kernel.org> |
|---|---|
| Date | 2017-06-22 21:50 +0200 |
| Subject | Re: [tip:sched/core] sched/fair: Spare idle load balancing on nohz_full CPUs |
| Message-ID | <tVgh4-Ba-7@gated-at.bofh.it> |
| In reply to | #1672653 |
* Frederic Weisbecker <fweisbec@gmail.com> wrote: > Hi Ingo, > > On Thu, Jun 22, 2017 at 04:11:53AM -0700, tip-bot for Frederic Weisbecker wrote: > > Commit-ID: 387bc8b5536eeb0a92f4b4ab553539eaea2ac0ba > > Gitweb: http://git.kernel.org/tip/387bc8b5536eeb0a92f4b4ab553539eaea2ac0ba > > Author: Frederic Weisbecker <fweisbec@gmail.com> > > AuthorDate: Mon, 19 Jun 2017 04:12:02 +0200 > > Committer: Ingo Molnar <mingo@kernel.org> > > CommitDate: Thu, 22 Jun 2017 11:30:02 +0200 > > > > sched/fair: Spare idle load balancing on nohz_full CPUs > > Thanks for applying the series! The two other patches are indeed good but > Rik and Mike have mitigated feelings about this very patch. I think we need to decouple > housekeeping from nohz_full before applying it. Is it possible to set it aside > for now? Well, if patches are forthcoming and the commit isn't buggy per se, we could have it with the note of it being improved further. Thanks, Ingo
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