From: Vincent Guittot <vincent.guittot@linaro.org>
To: Josh Don <joshdon@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
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>,
linux-kernel <linux-kernel@vger.kernel.org>,
Paul Turner <pjt@google.com>
Subject: Re: [PATCH v2] sched/fair: Do not set skip buddy up the sched hierarchy
Date: Fri, 6 Dec 2019 08:57:11 +0100 [thread overview]
Message-ID: <CAKfTPtBZUUtJ=ZvQOWmKx_1zUXtNoqcS0M85ouQmgi36xzfM2A@mail.gmail.com> (raw)
In-Reply-To: <20191204200623.198897-1-joshdon@google.com>
Hi Josh,
On Wed, 4 Dec 2019 at 21:06, Josh Don <joshdon@google.com> wrote:
>
> From: Venkatesh Pallipadi <venki@google.com>
>
> Setting skip buddy all the way up the hierarchy does not play well
> with intra-cgroup yield. One typical usecase of yield is when a
> thread in a cgroup wants to yield CPU to another thread within the
> same cgroup. For such a case, setting the skip buddy all the way up
> the hierarchy is counter-productive, as that results in CPU being
> yielded to a task in some other cgroup.
>
> So, limit the skip effect only to the task requesting it.
>
> Signed-off-by: Josh Don <joshdon@google.com>
There is a mismatch between the author Venkatesh Pallipadi and the
signoff Josh Don
If Venkatesh is the original author and you have then done some
modifications, your both signed-off should be there
Apart from that, the change makes sense to me
> ---
> v2: Only clear skip buddy on the current cfs_rq
>
> kernel/sched/fair.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 08a233e97a01..0b7a1958ad52 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4051,13 +4051,10 @@ static void __clear_buddies_next(struct sched_entity *se)
>
> static void __clear_buddies_skip(struct sched_entity *se)
> {
> - for_each_sched_entity(se) {
> - struct cfs_rq *cfs_rq = cfs_rq_of(se);
> - if (cfs_rq->skip != se)
> - break;
> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
>
> + if (cfs_rq->skip == se)
> cfs_rq->skip = NULL;
> - }
> }
>
> static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
> @@ -6552,8 +6549,15 @@ static void set_next_buddy(struct sched_entity *se)
>
> static void set_skip_buddy(struct sched_entity *se)
> {
> - for_each_sched_entity(se)
> - cfs_rq_of(se)->skip = se;
> + /*
> + * One typical usecase of yield is when a thread in a cgroup
> + * wants to yield CPU to another thread within the same cgroup.
> + * For such a case, setting the skip buddy all the way up the
> + * hierarchy is counter-productive, as that results in CPU being
> + * yielded to a task in some other cgroup. So, only set skip
> + * for the task requesting it.
> + */
> + cfs_rq_of(se)->skip = se;
> }
>
> /*
> --
> 2.24.0.393.g34dc348eaf-goog
>
next prev parent reply other threads:[~2019-12-06 7:57 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-04 20:06 [PATCH v2] sched/fair: Do not set skip buddy up the sched hierarchy Josh Don
2019-12-06 7:57 ` Vincent Guittot [this message]
2019-12-06 22:13 ` Josh Don
2019-12-09 9:18 ` Dietmar Eggemann
2019-12-12 22:19 ` Josh Don
2019-12-18 11:36 ` Dietmar Eggemann
2019-12-18 20:02 ` Josh Don
2019-12-19 0:14 ` [PATCH v3] " Josh Don
2019-12-26 15:05 ` Vincent Guittot
2020-02-25 1:50 ` Josh Don
2019-12-12 8:05 ` [PATCH v2] " Vincent Guittot
2019-12-17 19:58 ` Josh Don
2019-12-17 20:42 ` Peter Zijlstra
2019-12-17 21:00 ` Greg Kroah-Hartman
-- strict thread matches above, loose matches on Subject: below --
2019-11-04 14:54 [PATCH] " Vincent Guittot
2019-11-06 22:14 ` [PATCH v2] " Josh Don
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