From: Vincent Guittot <vincent.guittot@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH] sched/pelt: fix false running accounting in PELT
Date: Sat, 1 Jul 2017 07:09:43 +0200 [thread overview]
Message-ID: <CAKfTPtB__HHE2WuDuc43J1BoeYuP2vXw5u7NHpe99go9uubGBw@mail.gmail.com> (raw)
In-Reply-To: <1498831118-22672-1-git-send-email-vincent.guittot@linaro.org>
On 30 June 2017 at 15:58, Vincent Guittot <vincent.guittot@linaro.org> wrote:
> The running state is a subset of runnable state which means that running
> can't be set if runnable (weight) is cleared. There are corner cases
> where the current sched_entity has been already dequeued but cfs_rq->curr
> has not been updated yet and still points to the dequeued sched_entity.
> If ___update_load_avg is called at that time, weight will be 0 and running
> will be set which is not possible.
>
> This case happens during pick_next_task_fair() when a cfs_rq becomes idles.
> The current sched_entity has been dequeued so se->on_rq is cleared and
> cfs_rq->weight is null. But cfs_rq->curr still points to se (it will be
> cleared when picking the idle thread). Because the cfs_rq becomes idle,
> idle_balance() is called and ends up to call update_blocked_averages()
> with these wrong running and runnable states.
>
> Add a test in ___update_load_avg to correct the running state in this case.*
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
The v1 is just wrong. I have sent a v2 with correct patch
sorry for the disturb
Vincent
> ---
> kernel/sched/fair.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 008c514..5fdcb42 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2968,6 +2968,24 @@ ___update_load_avg(u64 now, int cpu, struct sched_avg *sa,
> sa->last_update_time += delta << 10;
>
> /*
> + * running is a subset of runnable (weight) so running can't be set if
> + * runnable is clear. But there are some corner cases where the current
> + * se has been already dequeued but cfs_rq->curr still points to it.
> + * This means that weight will be 0 but not running for a sched_entity
> + * but also for a cfs_rq if the latter becomes idle. As an example,
> + * this happens during idle_balance() which calls
> + * update_blocked_averages()
> + */
> + if (weight)
> + running = 1;
> +
> + /*
> + * Scale time to reflect the amount a computation effectively done
> + * during the time slot at current capacity
> + */
> + delta = scale_time(delta, cpu, sa, weight, running);
> +
> + /*
> * Now we know we crossed measurement unit boundaries. The *_avg
> * accrues by two steps:
> *
> --
> 2.7.4
>
next prev parent reply other threads:[~2017-07-01 5:10 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-30 13:58 [PATCH] sched/pelt: fix false running accounting in PELT Vincent Guittot
2017-07-01 5:06 ` [PATCH v2] sched/pelt: fix false running accounting Vincent Guittot
2017-07-04 7:27 ` Peter Zijlstra
2017-07-04 7:37 ` Vincent Guittot
2017-07-04 8:34 ` Peter Zijlstra
2017-07-04 9:12 ` Vincent Guittot
2017-07-04 9:44 ` Peter Zijlstra
2017-07-04 9:57 ` Vincent Guittot
2017-07-04 11:07 ` Peter Zijlstra
2017-08-10 12:07 ` [tip:sched/core] sched/pelt: Fix " tip-bot for Vincent Guittot
2017-07-01 5:09 ` Vincent Guittot [this message]
2017-07-01 16:57 ` [PATCH] sched/pelt: fix false running accounting in PELT kbuild test robot
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