From: Valentin Schneider <valentin.schneider@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>,
linux-kernel@vger.kernel.org, mingo@redhat.com,
peterz@infradead.org
Cc: pauld@redhat.com, srikar@linux.vnet.ibm.com,
quentin.perret@arm.com, dietmar.eggemann@arm.com,
Morten.Rasmussen@arm.com, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3] sched/fair: use utilization to select misfit task
Date: Fri, 2 Aug 2019 15:27:18 +0100 [thread overview]
Message-ID: <af73850c-5f62-3688-8892-907a84cabafc@arm.com> (raw)
In-Reply-To: <1564750572-20251-1-git-send-email-vincent.guittot@linaro.org>
On 02/08/2019 13:56, Vincent Guittot wrote:
> utilization is used to detect a misfit task but the load is then used to
> select the task on the CPU which can lead to select a small task with
> high weight instead of the task that triggered the misfit migration.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> Keep tracking load instead of utilization but check that
> task doesn't fit CPU's capacity when selecting the task to detach as
> suggested by Valentin
>
I find that one much better :) The very same fix could be applied
regardless of the rework, so FWIW (providing the changelog gets a bit
clearer - maybe squash the comment in it):
Acked-by: Valentin Schneider <valentin.schneider@arm.com>
One more thing though: we actually face the same problem in active balance,
i.e. the misfit task could sleep/get preempted before the CPU stopper
actually runs, and that latter would migrate $random.
I was thinking of passing the lb_env to stop_one_cpu_nowait() - we'd have
to rebuild it in active_load_balance_cpu_stop() anyway, but we could copy
things like env.migration_type so that we remember that we should be
picking a misfit task and have a similar detach guard.
Sadly, the lb_env struct is on load_balance()'s stack, and that's a nowait
call :/
Peter/Thomas, would there be much hate in adding some sort of flags field
to struct cpu_stop_work? Or if you see a better alternative, I'm all ears.
> kernel/sched/fair.c | 12 +++---------
> 1 file changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 53e64a7..8496118 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7487,15 +7487,9 @@ static int detach_tasks(struct lb_env *env)
> break;
>
> case migrate_misfit:
> - load = task_h_load(p);
> -
> - /*
> - * utilization of misfit task might decrease a bit
> - * since it has been recorded. Be conservative in the
> - * condition.
> - */
> - if (load < env->imbalance)
> - goto next;
> + /* This is not a misfit task */
> + if (task_fits_capacity(p, capacity_of(env->src_cpu)))
> + goto next;
>
> env->imbalance = 0;
> break;
>
next prev parent reply other threads:[~2019-08-02 14:27 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 14:40 [PATCH v2 0/8] sched/fair: rework the CFS load balance Vincent Guittot
2019-08-01 14:40 ` [PATCH v2 1/8] sched/fair: clean up asym packing Vincent Guittot
2019-08-01 14:40 ` [PATCH v2 2/8] sched/fair: rename sum_nr_running to sum_h_nr_running Vincent Guittot
2019-08-01 14:40 ` [PATCH v2 3/8] sched/fair: remove meaningless imbalance calculation Vincent Guittot
2019-08-01 14:40 ` [PATCH v2 4/8] sched/fair: rework load_balance Vincent Guittot
2019-08-05 17:07 ` Valentin Schneider
2019-08-26 9:26 ` Vincent Guittot
2019-08-28 10:25 ` Valentin Schneider
2019-08-06 15:56 ` Peter Zijlstra
2019-08-26 9:31 ` Vincent Guittot
2019-08-06 17:17 ` Valentin Schneider
2019-08-07 11:16 ` Valentin Schneider
2019-08-26 10:11 ` Vincent Guittot
2019-08-28 14:19 ` Valentin Schneider
2019-08-29 14:26 ` Vincent Guittot
2019-08-30 14:33 ` Valentin Schneider
2019-08-01 14:40 ` [PATCH v2 5/8] sched/fair: use rq->nr_running when balancing load Vincent Guittot
2019-08-01 14:40 ` [PATCH v2 6/8] sched/fair: use load instead of runnable load Vincent Guittot
2019-08-06 16:07 ` Peter Zijlstra
2019-08-26 15:45 ` Vincent Guittot
2019-08-01 14:40 ` [PATCH v2 7/8] sched/fair: evenly spread tasks when not overloaded Vincent Guittot
2019-08-01 14:40 ` [PATCH v2 8/8] sched/fair: use utilization to select misfit task Vincent Guittot
2019-08-01 16:27 ` Valentin Schneider
2019-08-02 8:29 ` Vincent Guittot
2019-08-02 10:49 ` Valentin Schneider
2019-08-02 12:56 ` [PATCH v3] " Vincent Guittot
2019-08-02 14:27 ` Valentin Schneider [this message]
2019-08-05 11:01 ` Valentin Schneider
2019-08-29 19:23 ` [PATCH v2 0/8] sched/fair: rework the CFS load balance Phil Auld
2019-08-30 6:46 ` Vincent Guittot
[not found] ` <20190809052124.13016-1-hdanton@sina.com>
2019-09-02 13:07 ` [PATCH v2 5/8] sched/fair: use rq->nr_running when balancing load Vincent Guittot
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