From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Li Aubrey <aubrey.li@linux.intel.com>,
Qais Yousef <qais.yousef@arm.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/4] sched/fair: Merge select_idle_core/cpu()
Date: Wed, 27 Jan 2021 14:07:50 +0100 [thread overview]
Message-ID: <CAKfTPtB=vh0FzszeOS5ND4Voq3ck2AQgruF-4zC-K1hSSsbT_A@mail.gmail.com> (raw)
In-Reply-To: <20210127120245.GC3592@techsingularity.net>
On Wed, 27 Jan 2021 at 13:02, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Wed, Jan 27, 2021 at 11:43:22AM +0100, Vincent Guittot wrote:
> > > @@ -6149,18 +6161,31 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> > > }
> > >
> > > for_each_cpu_wrap(cpu, cpus, target) {
> > > - if (!--nr)
> > > - return -1;
> > > - if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
> > > - break;
> > > + if (smt) {
> > > + i = select_idle_core(p, cpu, cpus, &idle_cpu);
> > > + if ((unsigned int)i < nr_cpumask_bits)
> > > + return i;
> > > +
> > > + } else {
> > > + if (!--nr)
> > > + return -1;
> > > + i = __select_idle_cpu(cpu);
> >
> > you should use idle_cpu directly instead of this intermediate i variable
> >
> > + idle_cpu = __select_idle_cpu(cpu);
> > + if ((unsigned int)idle_cpu < nr_cpumask_bits)
> > + break;
> >
> > Apart ths small comment above, the patch looks good to me and I
> > haven't any performance regression anymore
> >
>
> It's matching the code sequence in the SMT block. If we are going to make
> that change, then go the full way with this?
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 52a650aa2108..01e40e36c386 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6129,7 +6129,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
> static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target)
> {
> struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
> - int i, cpu, idle_cpu = -1, nr = INT_MAX;
> + int cpu, idle_cpu = -1, nr = INT_MAX;
> bool smt = test_idle_cores(target, false);
> int this = smp_processor_id();
> struct sched_domain *this_sd;
> @@ -6162,18 +6162,16 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>
> for_each_cpu_wrap(cpu, cpus, target) {
> if (smt) {
> - i = select_idle_core(p, cpu, cpus, &idle_cpu);
> - if ((unsigned int)i < nr_cpumask_bits)
> - return i;
> + idle_cpu = select_idle_core(p, cpu, cpus, &idle_cpu);
but how do you differentiate idle core (return value) and an idle cpu
in the core set in &idle_cpu
You will return as soon as a cpu is idle and before testing all cores
> + if ((unsigned int)idle_cpu < nr_cpumask_bits)
> + return idle_cpu;
>
> } else {
> if (!--nr)
> return -1;
> - i = __select_idle_cpu(cpu);
> - if ((unsigned int)i < nr_cpumask_bits) {
> - idle_cpu = i;
> + idle_cpu = __select_idle_cpu(cpu);
> + if ((unsigned int)idle_cpu < nr_cpumask_bits)
> break;
> - }
> }
> }
>
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2021-01-27 13:11 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 8:59 [PATCH v4 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-25 8:59 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2021-01-25 8:59 ` [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
2021-01-27 10:39 ` Vincent Guittot
2021-01-25 8:59 ` [PATCH 3/4] sched/fair: Remove select_idle_smt() Mel Gorman
2021-01-27 10:39 ` Vincent Guittot
2021-02-17 13:17 ` [tip: sched/core] " tip-bot2 for Mel Gorman
2021-01-25 8:59 ` [PATCH 4/4] sched/fair: Merge select_idle_core/cpu() Mel Gorman
2021-01-27 10:43 ` Vincent Guittot
2021-01-27 12:02 ` Mel Gorman
2021-01-27 13:07 ` Vincent Guittot [this message]
2021-01-27 13:21 ` Mel Gorman
2021-01-27 13:26 ` Vincent Guittot
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-27 13:52 ` [PATCH 4/4] sched/fair: Merge select_idle_core/cpu() Mel Gorman
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