From: Yuyang Du <yuyang.du@intel.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: [PATCH v3] sched: fix first task of a task group is attached twice
Date: Tue, 31 May 2016 08:44:00 +0800 [thread overview]
Message-ID: <20160531004400.GO18670@intel.com> (raw)
In-Reply-To: <CAKfTPtAoPL_gVgM9t2E_7UTZxahypb14zpU7e8WdK+=ae5v+WQ@mail.gmail.com>
On Tue, May 31, 2016 at 09:28:30AM +0200, Vincent Guittot wrote:
> Hi Yuyang,
>
> On 30 May 2016 at 21:48, Yuyang Du <yuyang.du@intel.com> wrote:
> > On Mon, May 30, 2016 at 05:52:20PM +0200, Vincent Guittot wrote:
> >> The cfs_rq->avg.last_update_time is initialize to 0 with the main effect
> >> that the 1st sched_entity that will be attached, will keep its
> >> last_update_time set to 0 and will attached once again during the
> >> enqueue.
> >> Initialize cfs_rq->avg.last_update_time to 1 instead.
> >>
> >> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> >> ---
> >>
> >> v3:
> >> - add initialization of load_last_update_time_copy for not 64bits system
> >> - move init into init_cfs_rq
> >>
> >> v2:
> >> - rq_clock_task(rq_of(cfs_rq)) can't be used because lock is not held
> >>
> >> kernel/sched/fair.c | 10 ++++++++++
> >> 1 file changed, 10 insertions(+)
> >>
> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >> index 218f8e8..86be9c1 100644
> >> --- a/kernel/sched/fair.c
> >> +++ b/kernel/sched/fair.c
> >> @@ -8459,6 +8459,16 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
> >> cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
> >> #endif
> >> #ifdef CONFIG_SMP
> >> + /*
> >> + * Set last_update_time to something different from 0 to make
> >> + * sure the 1st sched_entity will not be attached twice:once
> >> + * when attaching the task to the group and one more time when
> >> + * enqueueing the task.
> >> + */
> >
> > The first time: "once when attaching the task to the group".
> >
> > That attaching is purely wrong, but will not have any effect (at least
> > load/util wise), because the task will later be inited in
> > init_entity_runnable_average().
>
> This patch is not related to the init of a task but related to the
> init of the cfs_rq and to what happen with the 1st task that is
> enqueued on it.
>
> Lets take a task A that has already been scheduled on other cfs_rq so
> its se->avg.last_update_time is different from 0.
I understand it, finally, :)
> Create a new task group TGB
> At creation, the cfs_rq->avg.last_update_time of this TGB is set to 0.
>
> Now move task A on TGB.
> A is attached to TGB so se->avg.last_update_time =
> cfs_rq->avg.last_update_time which is 0
> A is then enqueued on th cfs_rq and because se->avg.last_update_time
> == 0, A will be attached one more time on the cfs_rq
>
> This patch set cfs_rq->avg.last_update_time to 1 at creation so the
> 1st time that A is attached to TGB, se->avg.last_update_time =
> cfs_rq->avg.last_update_time = 1 and A will not bve attached one more
> time during the enqueue.
next prev parent reply other threads:[~2016-05-31 8:41 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-24 13:08 [PATCH] sched: fix first task of a task group is attached twice Vincent Guittot
2016-05-25 15:01 ` [PATCH v2] " Vincent Guittot
2016-05-25 22:38 ` Yuyang Du
2016-05-26 8:26 ` Vincent Guittot
2016-05-26 0:40 ` Yuyang Du
2016-05-26 8:51 ` Vincent Guittot
2016-05-27 15:48 ` Dietmar Eggemann
2016-05-27 17:16 ` Vincent Guittot
2016-05-27 20:38 ` Dietmar Eggemann
2016-05-30 7:04 ` Vincent Guittot
2016-05-30 15:52 ` [PATCH v3] " Vincent Guittot
2016-05-30 19:48 ` Yuyang Du
2016-05-31 7:28 ` Vincent Guittot
2016-05-31 0:44 ` Yuyang Du [this message]
2016-06-01 15:31 ` Dietmar Eggemann
2016-06-01 15:54 ` Vincent Guittot
2016-06-06 19:32 ` Dietmar Eggemann
2016-06-07 7:35 ` Vincent Guittot
2016-06-15 19:19 ` Yuyang Du
2016-06-16 7:12 ` Vincent Guittot
2016-06-15 23:24 ` Yuyang Du
2016-06-16 9:42 ` Vincent Guittot
2016-05-30 15:54 ` [PATCH v2] " Vincent Guittot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160531004400.GO18670@intel.com \
--to=yuyang.du@intel.com \
--cc=dietmar.eggemann@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=vincent.guittot@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).