From: Mel Gorman <mgorman@techsingularity.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Kernel Team <kernel-team@fb.com>, Ingo Molnar <mingo@kernel.org>,
Valentin Schneider <valentin.schneider@arm.com>
Subject: Re: [PATCH v3] sched/fair: bring back select_idle_smt, but differently
Date: Wed, 7 Apr 2021 11:47:17 +0100 [thread overview]
Message-ID: <20210407104717.GD3697@techsingularity.net> (raw)
In-Reply-To: <YG2GMW0EjsqqnET6@hirez.programming.kicks-ass.net>
On Wed, Apr 07, 2021 at 12:15:13PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 07, 2021 at 10:41:06AM +0100, Mel Gorman wrote:
>
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -6112,6 +6112,27 @@ static int select_idle_core(struct task_
> > > return -1;
> > > }
> > >
> > > +/*
> > > + * Scan the local SMT mask for idle CPUs.
> > > + */
> > > +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
> > > +{
> > > + int cpu;
> > > +
> > > + if (!static_branch_likely(&sched_smt_present))
> > > + return -1;
> > > +
> > > + for_each_cpu(cpu, cpu_smt_mask(target)) {
> > > + if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
> > > + !cpumask_test_cpu(cpu, sched_domain_span(sd)))
> > > + continue;
> >
> > While I know that !cpumask_test_cpu(cpu, sched_domain_span(sd)) was
> > done previously, I found it hard to believe that the test matters. If
> > target/prev share a the LLC domain, why would the SMT siblings *not*
> > share a LLC?
>
> I think the reason for it is that a cpuset might have split the siblings
> apart and disabled load-balancing across them or something.
>
> Then the affinity mask can still cross the partition, but we shouldn't
> ever move into it through balancing.
Ok, cpusets do split domains. I can't imagine the logic of splitting SMT
siblings across cpusets but if it's possible, it has to be checked and
protecting that with cpusets_enabled() would be a little overkill and
possibly miss some other corner case :(
Thanks.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2021-04-07 10:48 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-21 19:03 [PATCH v2] sched/fair: bring back select_idle_smt, but differently Rik van Riel
2021-03-22 11:03 ` Mel Gorman
2021-03-22 15:07 ` Rik van Riel
2021-03-22 15:33 ` Mel Gorman
2021-03-23 2:08 ` Rik van Riel
2021-03-26 19:19 ` [PATCH v3] " Rik van Riel
2021-03-28 15:36 ` Mel Gorman
2021-04-06 15:10 ` Vincent Guittot
2021-04-06 15:26 ` Rik van Riel
2021-04-06 15:31 ` Vincent Guittot
2021-04-06 15:33 ` Vincent Guittot
2021-04-06 15:55 ` Rik van Riel
2021-04-06 16:13 ` Vincent Guittot
2021-04-07 7:17 ` Peter Zijlstra
2021-04-07 9:41 ` Mel Gorman
2021-04-07 10:15 ` Peter Zijlstra
2021-04-07 10:47 ` Mel Gorman [this message]
2021-04-07 12:10 ` Peter Zijlstra
2021-04-07 9:42 ` Vincent Guittot
2021-04-07 9:54 ` Peter Zijlstra
2021-04-07 9:57 ` Vincent Guittot
2021-04-07 10:19 ` Peter Zijlstra
2021-04-07 10:24 ` Vincent Guittot
2021-04-08 15:52 ` Rik van Riel
2021-04-09 11:24 ` [tip: sched/core] sched/fair: Bring back select_idle_smt(), " tip-bot2 for Rik van Riel
2021-04-09 16:14 ` tip-bot2 for Rik van Riel
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