From: Vincent Guittot <vincent.guittot@linaro.org>
To: Julia Lawall <Julia.Lawall@inria.fr>
Cc: Ingo Molnar <mingo@redhat.com>,
kernel-janitors@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Gilles Muller <Gilles.Muller@inria.fr>
Subject: Re: [PATCH] sched/fair: check for idle core
Date: Wed, 21 Oct 2020 09:29:46 +0200 [thread overview]
Message-ID: <CAKfTPtB41JopBq0CZVvo16N1u+2Smmc1TamJXkbTVj-pRJeHzA@mail.gmail.com> (raw)
In-Reply-To: <1603211879-1064-1-git-send-email-Julia.Lawall@inria.fr>
Hi Julia,
On Tue, 20 Oct 2020 at 19:21, Julia Lawall <Julia.Lawall@inria.fr> wrote:
>
> On a thread wakeup, the change [1] from runnable load average to load
> average for comparing candidate cores means that recent short-running
> daemons on the core where a thread ran previously can be considered to
> have a higher load than the core performing the wakeup, even when the
> core where the thread ran previously is currently idle. This can
> cause a thread to migrate, taking the place of some other thread that
> is about to wake up, and so on. To avoid unnecessary migrations,
> extend wake_affine_idle to check whether the core where the thread
> previously ran is currently idle, and if so return that core as the
> target.
>
> [1] commit 11f10e5420f6ce ("sched/fair: Use load instead of runnable
> load in wakeup path")
>
> This particularly has an impact when using passive (intel_cpufreq)
> power management, where kworkers run every 0.004 seconds on all cores,
> increasing the likelihood that an idle core will be considered to have
> a load.
>
> The following numbers were obtained with the benchmarking tool
> hyperfine (https://github.com/sharkdp/hyperfine) on the NAS parallel
> benchmarks (https://www.nas.nasa.gov/publications/npb.html). The
> tests were run on an 80-core Intel(R) Xeon(R) CPU E7-8870 v4 @
> 2.10GHz. Active (intel_pstate) and passive (intel_cpufreq) power
> management were used. Times are in seconds. All experiments use all
> 160 hardware threads.
>
> v5.9/active v5.9+patch/active
> bt.C.c 24.725724+-0.962340 23.349608+-1.607214
> lu.C.x 29.105952+-4.804203 25.249052+-5.561617
> sp.C.x 31.220696+-1.831335 30.227760+-2.429792
> ua.C.x 26.606118+-1.767384 25.778367+-1.263850
>
> v5.9/passive v5.9+patch/passive
> bt.C.c 25.330360+-1.028316 23.544036+-1.020189
> lu.C.x 35.872659+-4.872090 23.719295+-3.883848
> sp.C.x 32.141310+-2.289541 29.125363+-0.872300
> ua.C.x 29.024597+-1.667049 25.728888+-1.539772
>
> On the smaller data sets (A and B) and on the other NAS benchmarks
> there is no impact on performance.
>
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Reviewed-by Vincent Guittot <vincent.guittot@linaro.org>
>
> ---
> kernel/sched/fair.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index aa4c6227cd6d..9b23dad883ee 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5804,6 +5804,9 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
> if (sync && cpu_rq(this_cpu)->nr_running == 1)
> return this_cpu;
>
> + if (available_idle_cpu(prev_cpu))
> + return prev_cpu;
> +
> return nr_cpumask_bits;
> }
>
>
next prev parent reply other threads:[~2020-10-21 7:30 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 16:37 [PATCH] sched/fair: check for idle core Julia Lawall
2020-10-21 7:29 ` Vincent Guittot [this message]
2020-10-21 11:13 ` Peter Zijlstra
2020-10-21 12:27 ` Vincent Guittot
2020-10-21 11:20 ` Mel Gorman
2020-10-21 11:56 ` Julia Lawall
2020-10-21 12:19 ` Peter Zijlstra
2020-10-21 12:42 ` Julia Lawall
2020-10-21 12:52 ` Peter Zijlstra
2020-10-21 13:43 ` Julia Lawall
2020-10-21 18:18 ` Rafael J. Wysocki
2020-10-21 18:15 ` Rafael J. Wysocki
2020-10-21 19:47 ` Julia Lawall
2020-10-21 20:25 ` Rafael J. Wysocki
2020-10-21 13:10 ` Peter Zijlstra
2020-10-21 18:11 ` Rafael J. Wysocki
2020-10-22 4:41 ` Viresh Kumar
2020-10-22 7:11 ` Peter Zijlstra
2020-10-22 10:47 ` Viresh Kumar
2020-10-22 11:45 ` Rafael J. Wysocki
2020-10-22 12:02 ` default cpufreq gov, was: " Peter Zijlstra
2020-10-22 12:19 ` Rafael J. Wysocki
2020-10-22 12:29 ` Peter Zijlstra
2020-10-22 14:52 ` Mel Gorman
2020-10-22 14:58 ` Colin Ian King
2020-10-22 15:12 ` Phil Auld
2020-10-22 16:35 ` Mel Gorman
2020-10-22 17:59 ` Rafael J. Wysocki
2020-10-22 20:32 ` Mel Gorman
2020-10-22 20:39 ` Phil Auld
2020-10-22 15:25 ` Peter Zijlstra
2020-10-22 15:55 ` Rafael J. Wysocki
2020-10-22 16:29 ` Mel Gorman
2020-10-22 20:10 ` Giovanni Gherdovich
2020-10-22 20:16 ` Giovanni Gherdovich
2020-10-23 7:03 ` Peter Zijlstra
2020-10-23 17:46 ` Tom Lendacky
2020-10-26 19:52 ` Fontenot, Nathan
2020-10-22 15:45 ` A L
2020-10-22 15:55 ` Vincent Guittot
2020-10-23 5:11 ` Viresh Kumar
2020-10-22 16:23 ` [PATCH] cpufreq: Avoid configuring old governors as default with intel_pstate Rafael J. Wysocki
2020-10-23 6:17 ` Viresh Kumar
2020-10-23 11:59 ` Rafael J. Wysocki
2020-10-23 15:15 ` [PATCH v2] " Rafael J. Wysocki
2020-10-27 3:01 ` Viresh Kumar
2020-10-27 11:11 ` default cpufreq gov, was: [PATCH] sched/fair: check for idle core Qais Yousef
2020-10-27 11:26 ` Valentin Schneider
2020-10-27 11:42 ` Qais Yousef
2020-10-27 11:48 ` Viresh Kumar
2020-10-23 6:12 ` Viresh Kumar
2020-10-23 15:06 ` Rafael J. Wysocki
2020-10-27 3:01 ` Viresh Kumar
2020-10-22 11:21 ` AW: " Walter Harms
2020-10-21 12:28 ` Mel Gorman
2020-10-21 12:25 ` Vincent Guittot
2020-10-21 12:47 ` Mel Gorman
2020-10-21 12:56 ` Julia Lawall
2020-10-21 13:18 ` Mel Gorman
2020-10-21 13:24 ` Julia Lawall
2020-10-21 15:08 ` Mel Gorman
2020-10-21 15:18 ` Julia Lawall
2020-10-21 15:23 ` Vincent Guittot
2020-10-21 15:33 ` Julia Lawall
2020-10-21 15:19 ` Vincent Guittot
2020-10-21 17:00 ` Mel Gorman
2020-10-21 17:39 ` Julia Lawall
2020-10-21 13:48 ` Julia Lawall
2020-10-21 15:26 ` Mel Gorman
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