From: Subhra Mazumdar <subhra.mazumdar@oracle.com>
To: Viresh Kumar <viresh.kumar@linaro.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
tkjos@google.com, Daniel Lezcano <daniel.lezcano@linaro.org>,
quentin.perret@linaro.org, chris.redpath@arm.com,
steven.sistare@oracle.com, songliubraving@fb.com
Subject: Re: [PATCH V3 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found
Date: Fri, 28 Jun 2019 18:16:28 -0700 [thread overview]
Message-ID: <32bd769c-b692-8896-5cc9-d19ab0a23abb@oracle.com> (raw)
In-Reply-To: <eeafa25fdeb6f6edd5b2da716bc8f0ba7708cbcf.1561523542.git.viresh.kumar@linaro.org>
On 6/25/19 10:06 PM, Viresh Kumar wrote:
> We try to find an idle CPU to run the next task, but in case we don't
> find an idle CPU it is better to pick a CPU which will run the task the
> soonest, for performance reason.
>
> A CPU which isn't idle but has only SCHED_IDLE activity queued on it
> should be a good target based on this criteria as any normal fair task
> will most likely preempt the currently running SCHED_IDLE task
> immediately. In fact, choosing a SCHED_IDLE CPU over a fully idle one
> shall give better results as it should be able to run the task sooner
> than an idle CPU (which requires to be woken up from an idle state).
>
> This patch updates both fast and slow paths with this optimization.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> kernel/sched/fair.c | 43 +++++++++++++++++++++++++++++++++----------
> 1 file changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1277adc3e7ed..2e0527fd468c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5376,6 +5376,15 @@ static struct {
>
> #endif /* CONFIG_NO_HZ_COMMON */
>
> +/* CPU only has SCHED_IDLE tasks enqueued */
> +static int sched_idle_cpu(int cpu)
> +{
> + struct rq *rq = cpu_rq(cpu);
> +
> + return unlikely(rq->nr_running == rq->cfs.idle_h_nr_running &&
> + rq->nr_running);
> +}
> +
Shouldn't this check if rq->curr is also sched idle? And why not drop the
rq->nr_running non zero check?
next prev parent reply other threads:[~2019-06-29 1:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-26 5:06 [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence of idle CPUs Viresh Kumar
2019-06-26 5:06 ` [PATCH V3 1/2] sched: Start tracking SCHED_IDLE tasks count in cfs_rq Viresh Kumar
2019-07-25 16:15 ` [tip:sched/core] sched/fair: " tip-bot for Viresh Kumar
2019-06-26 5:06 ` [PATCH V3 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found Viresh Kumar
2019-06-29 1:16 ` Subhra Mazumdar [this message]
2019-07-01 8:03 ` Viresh Kumar
2019-07-01 22:08 ` Subhra Mazumdar
2019-07-02 8:35 ` Peter Zijlstra
2019-07-02 16:32 ` Subhra Mazumdar
2019-07-25 16:16 ` [tip:sched/core] sched/fair: Fall back " tip-bot for Viresh Kumar
2019-07-01 13:43 ` [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence of idle CPUs Peter Zijlstra
2019-07-03 9:13 ` Viresh Kumar
2019-12-09 3:50 ` Wanpeng Li
2019-12-10 6:33 ` Viresh Kumar
2019-12-10 11:15 ` Wanpeng Li
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