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Date: Sun, 10 Oct 2021 00:50:57 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Tao Zhou <tao.zhou@...ux.dev> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira <bristot@...hat.com> Subject: Re: [PATCH] sched/fair: Check idle_cpu in select_idle_core/cpu() On Sun, Oct 10, 2021 at 02:09:41AM +0800, Tao Zhou wrote: > In select_idle_core(), the idle core returned may have no cpu > allowed. I think the idle core returned for the task is the one > that can be allowed to run. I insist on this semantics. > > In select_idle_cpu(), if select_idle_core() can not find the > idle core, one reason is that the core is not allowed for the > task, but the core itself is idle from the point of > sds->has_idle_cores. I insist on this semantics. > > No others, just two additional check. > --- > kernel/sched/fair.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index f6a05d9b5443..a44aca5095d3 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6213,7 +6213,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu > *idle_cpu = cpu; > } > > - if (idle) > + if (idle && *idle_cpu != -1) > return core; In that case, core would be nr_cpu_ids (==nr_cpumask_bits), and then the caller checks: (unsigned)i < nr_cpumask_bits > cpumask_andnot(cpus, cpus, cpu_smt_mask(core)); > @@ -6324,7 +6324,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > } > } > > - if (has_idle_core) > + if (has_idle_core && *idle_cpu != -1) > set_idle_cores(target, false); And this one I'm completely failing, why shouldn't we mark the core as non-idle when there is a single idle CPU found? That's just worng.
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