From: Mel Gorman <mgorman@techsingularity.net>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
"Li, Aubrey" <aubrey.li@linux.intel.com>,
vincent.guittot@linaro.org, linux-kernel@vger.kernel.org,
mingo@redhat.com, juri.lelli@redhat.com,
valentin.schneider@arm.com, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com,
tim.c.chen@linux.intel.com, benbjiang@gmail.com
Subject: Re: [RFC][PATCH 1/5] sched/fair: Fix select_idle_cpu()s cost accounting
Date: Fri, 8 Jan 2021 13:47:36 +0000 [thread overview]
Message-ID: <20210108134736.GC3592@techsingularity.net> (raw)
In-Reply-To: <20210108130110.cj3zqsnjdt5mg3uz@e107158-lin>
On Fri, Jan 08, 2021 at 01:01:10PM +0000, Qais Yousef wrote:
> On 01/08/21 10:27, Mel Gorman wrote:
> > for_each_cpu_wrap(cpu, cpus, target) {
> > - if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
> > + if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) {
> > + /* Adjust cost of a successful scan */
> > + loops <<= 2;
> > +
> > break;
> > + }
> >
> > - if (loops >= nr) {
> > + if (++loops >= nr) {
> > cpu = -1;
> > break;
> > }
> > - loops++;
>
> Random (out of the blue) comment.
>
> Now this will increment loops before the comparison/break. ie: we're
> effectively doing one iteration less IIRC. Should loops be initialized to
> 0 instead of 1?
>
Yep, although in practice it'll make little difference except after a
rapid phase change when avg_idle still appears high on a per-rq basis
yet the domain is fully busy with no idle CPUs.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2021-01-08 13:48 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-14 16:48 [RFC][PATCH 0/5] select_idle_sibling() wreckage Peter Zijlstra
2020-12-14 16:48 ` [RFC][PATCH 1/5] sched/fair: Fix select_idle_cpu()s cost accounting Peter Zijlstra
2020-12-15 3:36 ` Li, Aubrey
2020-12-15 7:59 ` Peter Zijlstra
2020-12-15 11:45 ` Mel Gorman
2020-12-15 12:13 ` Li, Aubrey
2021-01-08 10:27 ` Mel Gorman
2021-01-08 13:01 ` Qais Yousef
2021-01-08 13:47 ` Mel Gorman [this message]
2021-01-08 13:41 ` Vincent Guittot
2021-01-08 14:40 ` Mel Gorman
2021-01-08 15:10 ` Vincent Guittot
2021-01-08 16:14 ` Mel Gorman
2021-01-11 14:36 ` Vincent Guittot
2021-01-11 15:58 ` Mel Gorman
2021-01-08 19:45 ` Peter Zijlstra
2021-01-09 14:12 ` Mel Gorman
2021-01-11 14:39 ` Vincent Guittot
2021-01-08 19:49 ` Peter Zijlstra
2021-01-11 14:52 ` Vincent Guittot
2021-01-08 20:21 ` Peter Zijlstra
2021-01-09 13:59 ` Mel Gorman
2020-12-14 16:48 ` [RFC][PATCH 2/5] sched/fair: Make select_idle_cpu() proportional to cores Peter Zijlstra
2020-12-23 13:31 ` Vincent Guittot
2020-12-14 16:48 ` [RFC][PATCH 3/5] sched/fair: Remove select_idle_smt() Peter Zijlstra
2020-12-14 16:48 ` [RFC][PATCH 4/5] sched/fair: Merge select_idle_core/cpu() Peter Zijlstra
2020-12-14 16:48 ` [RFC][PATCH 5/5] sched/fair: SIS_PROP the idle core scan Peter Zijlstra
2020-12-16 12:59 ` [RFC][PATCH 0/5] select_idle_sibling() wreckage Li, Aubrey
2020-12-16 18:07 ` Vincent Guittot
2020-12-23 13:23 ` Vincent Guittot
2021-01-04 15:40 ` Mel Gorman
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