From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>,
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 5/5] sched/fair: Merge select_idle_core/cpu()
Date: Wed, 20 Jan 2021 10:58:10 +0100 [thread overview]
Message-ID: <CAKfTPtBP_Q_5-3_Upv2geuU-qNQ-2i8E71-pC+eZWJSN6qNyXg@mail.gmail.com> (raw)
In-Reply-To: <20210120095420.GU3592@techsingularity.net>
On Wed, 20 Jan 2021 at 10:54, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Wed, Jan 20, 2021 at 10:21:47AM +0100, Vincent Guittot wrote:
> > On Wed, 20 Jan 2021 at 10:12, Mel Gorman <mgorman@techsingularity.net> wrote:
> > >
> > > On Wed, Jan 20, 2021 at 02:00:18PM +0530, Gautham R Shenoy wrote:
> > > > > @@ -6157,18 +6169,31 @@ 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);
> > > > > + if ((unsigned int)i < nr_cpumask_bits) {
> > > > > + idle_cpu = i;
> > > > > + break;
> > > > > + }
> > > > > + }
> > > > > }
> > > > >
> > > > > - if (sched_feat(SIS_PROP)) {
> > > > > + if (smt)
> > > > > + set_idle_cores(this, false);
> > > >
> > > > Shouldn't we set_idle_cores(false) only if this was the last idle
> > > > core in the LLC ?
> > > >
> > >
> > > That would involve rechecking the cpumask bits that have not been
> > > scanned to see if any of them are an idle core. As the existance of idle
> > > cores can change very rapidly, it's not worth the cost.
> >
> > But don't we reach this point only if we scanned all CPUs and didn't
> > find an idle core ?
>
> Yes, but my understanding of Gauthams suggestion was to check if an
> idle core found was the last idle core available and set has_idle_cores
ok get it now
> to false in that case. I think this would be relatively expensive and
> possibly futile as returning the last idle core for this wakeup does not
> mean there will be no idle core on the next wakeup as other cores may go
> idle between wakeups.
I agree, this doesn't worth the added complexity
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2021-01-20 10:25 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 11:22 [PATCH v3 0/5] Scan for an idle sibling in a single pass Mel Gorman
2021-01-19 11:22 ` [PATCH 1/5] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2021-01-19 11:22 ` [PATCH 2/5] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
2021-01-19 11:22 ` [PATCH 3/5] sched/fair: Make select_idle_cpu() proportional to cores Mel Gorman
2021-01-19 11:22 ` [PATCH 4/5] sched/fair: Remove select_idle_smt() Mel Gorman
2021-01-19 11:22 ` [PATCH 5/5] sched/fair: Merge select_idle_core/cpu() Mel Gorman
2021-01-20 8:30 ` Gautham R Shenoy
2021-01-20 9:12 ` Mel Gorman
2021-01-20 9:21 ` Vincent Guittot
2021-01-20 9:54 ` Mel Gorman
2021-01-20 9:58 ` Vincent Guittot [this message]
2021-01-20 13:55 ` Gautham R Shenoy
2021-01-19 11:33 ` [PATCH v3 0/5] Scan for an idle sibling in a single pass Vincent Guittot
2021-01-19 12:02 ` Mel Gorman
2021-01-22 9:30 ` Vincent Guittot
2021-01-22 10:14 ` Mel Gorman
2021-01-22 13:22 ` Vincent Guittot
2021-01-25 4:29 ` Li, Aubrey
2021-01-25 9:04 ` Mel Gorman
2021-01-25 11:37 ` Li, Aubrey
2021-01-25 11:46 ` Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2021-01-15 10:08 [PATCH v2 " Mel Gorman
2021-01-15 10:08 ` [PATCH 5/5] sched/fair: Merge select_idle_core/cpu() Mel Gorman
2021-01-18 12:55 ` Li, Aubrey
2021-01-18 14:41 ` Mel Gorman
2021-01-11 15:50 [PATCH 0/5] Scan for an idle sibling in a single pass Mel Gorman
2021-01-11 15:50 ` [PATCH 5/5] sched/fair: Merge select_idle_core/cpu() Mel Gorman
2021-01-13 17:03 ` Vincent Guittot
2021-01-14 9:35 ` Mel Gorman
2021-01-14 13:25 ` Vincent Guittot
2021-01-14 13:53 ` Mel Gorman
2021-01-14 15:44 ` Vincent Guittot
2021-01-14 17:18 ` Mel Gorman
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