From: Yuyang Du <yuyang.du@intel.com>
To: Steve Muckle <steve.muckle@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Juri Lelli <Juri.Lelli@arm.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: PELT initial task load and wake_up_new_task()
Date: Tue, 15 Dec 2015 10:24:32 +0800 [thread overview]
Message-ID: <20151215022432.GG28098@intel.com> (raw)
In-Reply-To: <566F61AA.4020904@linaro.org>
On Mon, Dec 14, 2015 at 04:41:14PM -0800, Steve Muckle wrote:
> Hi Yuyang,
>
> On 12/13/2015 11:13 AM, Yuyang Du wrote:
> > Hi Steve,
> >
> > On Fri, Dec 11, 2015 at 06:01:45PM -0800, Steve Muckle wrote:
> >> In init_entity_runnable_average() the last_update_time is initialized to
> >> zero. The task is given max load and utilization as a pessimistic
> >> initial estimate.
> >>
> >> But if in wake_up_new_task() the task is placed on a CPU other than
> >> where it was created, __update_load_avg() will be called via
> >> set_task_cpu() -> migrate_task_rq_fair() -> remove_entity_load_avg().
> >>
> >> Since last_update_time is zero the delta will be huge and the task's
> >> load will be entirely decayed away before it is enqueued at the
> >> destination CPU.
> >
> > Since the new task's last_update_time is equal to 0, it will not be decayed.
>
> Can you point me to the code for that logic? I don't see anything that
> prevents the decay when a newly woken task is placed on a different CPU
> via the call chain I mentioned above. My testing also shows the load
> being decayed to zero.
>
You may search the last_update_time, and see it would be treated differently
if it is 0. Hope this may be helpful.
next prev parent reply other threads:[~2015-12-15 10:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-12 2:01 PELT initial task load and wake_up_new_task() Steve Muckle
2015-12-13 19:13 ` Yuyang Du
2015-12-15 0:41 ` Steve Muckle
2015-12-15 2:24 ` Yuyang Du [this message]
2015-12-15 18:45 ` Steve Muckle
2015-12-15 23:55 ` Yuyang Du
2015-12-16 7:58 ` [PATCH] sched: Fix new task's load avg removed from source CPU in kbuild test robot
2015-12-17 2:50 ` PELT initial task load and wake_up_new_task() Steve Muckle
2015-12-16 23:34 ` Yuyang Du
2015-12-17 9:43 ` Peter Zijlstra
2015-12-17 2:16 ` Yuyang Du
2016-01-06 18:49 ` [tip:sched/core] sched/fair: Fix new task' s load avg removed from source CPU in wake_up_new_task() tip-bot for Yuyang Du
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