From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Phil Auld <pauld@redhat.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Quentin Perret <quentin.perret@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
Hillf Danton <hdanton@sina.com>
Subject: Re: [PATCH v3 04/10] sched/fair: rework load_balance
Date: Wed, 2 Oct 2019 11:24:51 +0200 [thread overview]
Message-ID: <1aea9422-a164-ceb6-5b8f-da728718bab9@arm.com> (raw)
In-Reply-To: <CAKfTPtAOErKG3XJDbLQEGgqs485ad4R7xc3k1UA9h5092GnkqQ@mail.gmail.com>
On 02/10/2019 10:23, Vincent Guittot wrote:
> On Tue, 1 Oct 2019 at 18:53, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>
>> On 01/10/2019 10:14, Vincent Guittot wrote:
>>> On Mon, 30 Sep 2019 at 18:24, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>>>
>>>> Hi Vincent,
>>>>
>>>> On 19/09/2019 09:33, Vincent Guittot wrote:
>>
> [...]
>
>>
>>>>> + if (busiest->group_weight == 1 || sds->prefer_sibling) {
>>>>> + /*
>>>>> + * When prefer sibling, evenly spread running tasks on
>>>>> + * groups.
>>>>> + */
>>>>> + env->balance_type = migrate_task;
>>>>> + env->imbalance = (busiest->sum_h_nr_running - local->sum_h_nr_running) >> 1;
>>>>> + return;
>>>>> + }
>>>>> +
>>>>> + /*
>>>>> + * If there is no overload, we just want to even the number of
>>>>> + * idle cpus.
>>>>> + */
>>>>> + env->balance_type = migrate_task;
>>>>> + env->imbalance = max_t(long, 0, (local->idle_cpus - busiest->idle_cpus) >> 1);
>>>>
>>>> Why do we need a max_t(long, 0, ...) here and not for the 'if
>>>> (busiest->group_weight == 1 || sds->prefer_sibling)' case?
>>>
>>> For env->imbalance = (busiest->sum_h_nr_running - local->sum_h_nr_running) >> 1;
>>>
>>> either we have sds->prefer_sibling && busiest->sum_nr_running >
>>> local->sum_nr_running + 1
>>
>> I see, this corresponds to
>>
>> /* Try to move all excess tasks to child's sibling domain */
>> if (sds.prefer_sibling && local->group_type == group_has_spare &&
>> busiest->sum_h_nr_running > local->sum_h_nr_running + 1)
>> goto force_balance;
>>
>> in find_busiest_group, I assume.
>
> yes. But it seems that I missed a case:
>
> prefer_sibling is set
> busiest->sum_h_nr_running <= local->sum_h_nr_running + 1 so we skip
> goto force_balance above
> But env->idle != CPU_NOT_IDLE and local->idle_cpus >
> (busiest->idle_cpus + 1) so we also skip goto out_balance and finally
> call calculate_imbalance()
>
> in calculate_imbalance with prefer_sibling set, imbalance =
> (busiest->sum_h_nr_running - local->sum_h_nr_running) >> 1;
>
> so we probably want something similar to max_t(long, 0,
> (busiest->sum_h_nr_running - local->sum_h_nr_running) >> 1)
Makes sense.
Caught a couple of
[ 369.310464] 0-3->4-7 2->5 env->imbalance = 2147483646
[ 369.310796] 0-3->4-7 2->4 env->imbalance = 2147483647
in this if condition on h620 running hackbench.
next prev parent reply other threads:[~2019-10-02 9:25 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-19 7:33 [PATCH v3 0/8] sched/fair: rework the CFS load balance Vincent Guittot
2019-09-19 7:33 ` [PATCH v3 01/10] sched/fair: clean up asym packing Vincent Guittot
2019-09-27 23:57 ` Rik van Riel
2019-09-19 7:33 ` [PATCH v3 02/10] sched/fair: rename sum_nr_running to sum_h_nr_running Vincent Guittot
2019-09-27 23:59 ` Rik van Riel
2019-10-01 17:11 ` Valentin Schneider
2019-09-19 7:33 ` [PATCH v3 03/10] sched/fair: remove meaningless imbalance calculation Vincent Guittot
2019-09-28 0:05 ` Rik van Riel
2019-10-01 17:12 ` Valentin Schneider
2019-10-02 6:28 ` Vincent Guittot
2019-09-19 7:33 ` [PATCH v3 04/10] sched/fair: rework load_balance Vincent Guittot
2019-09-30 1:12 ` Rik van Riel
2019-09-30 7:44 ` Vincent Guittot
2019-09-30 16:24 ` Dietmar Eggemann
2019-10-01 8:14 ` Vincent Guittot
2019-10-01 16:52 ` Dietmar Eggemann
2019-10-02 6:44 ` Vincent Guittot
2019-10-02 9:21 ` Dietmar Eggemann
2019-10-08 13:02 ` Peter Zijlstra
2019-10-02 8:23 ` Vincent Guittot
2019-10-02 9:24 ` Dietmar Eggemann [this message]
2019-10-01 8:15 ` Dietmar Eggemann
2019-10-01 9:14 ` Vincent Guittot
2019-10-01 16:57 ` Dietmar Eggemann
2019-10-01 17:47 ` Valentin Schneider
2019-10-02 8:30 ` Vincent Guittot
2019-10-02 10:47 ` Valentin Schneider
2019-10-08 14:16 ` Peter Zijlstra
2019-10-08 14:34 ` Valentin Schneider
2019-10-08 15:30 ` Vincent Guittot
2019-10-08 15:48 ` Valentin Schneider
2019-10-08 17:39 ` Peter Zijlstra
2019-10-08 18:45 ` Vincent Guittot
2019-10-08 16:33 ` Peter Zijlstra
2019-10-08 16:39 ` Valentin Schneider
2019-10-08 17:36 ` Valentin Schneider
2019-10-08 17:55 ` Peter Zijlstra
2019-10-08 18:47 ` Vincent Guittot
2019-10-16 7:21 ` Parth Shah
2019-10-16 11:56 ` Vincent Guittot
2019-10-18 5:34 ` Parth Shah
2019-09-19 7:33 ` [PATCH v3 05/10] sched/fair: use rq->nr_running when balancing load Vincent Guittot
2019-09-19 7:33 ` [PATCH v3 06/10] sched/fair: use load instead of runnable load in load_balance Vincent Guittot
2019-09-19 7:33 ` [PATCH v3 07/10] sched/fair: evenly spread tasks when not overloaded Vincent Guittot
2019-09-19 7:33 ` [PATCH v3 08/10] sched/fair: use utilization to select misfit task Vincent Guittot
2019-10-01 17:12 ` Valentin Schneider
2019-09-19 7:33 ` [PATCH v3 09/10] sched/fair: use load instead of runnable load in wakeup path Vincent Guittot
2019-10-07 15:14 ` Rik van Riel
2019-10-07 15:27 ` Vincent Guittot
2019-10-07 18:06 ` Rik van Riel
2019-09-19 7:33 ` [PATCH v3 10/10] sched/fair: optimize find_idlest_group Vincent Guittot
2019-10-08 14:32 ` [PATCH v3 0/8] sched/fair: rework the CFS load balance Phil Auld
2019-10-08 15:53 ` Vincent Guittot
2019-10-09 19:33 ` Phil Auld
2019-10-10 8:20 ` Vincent Guittot
2019-10-16 7:21 ` Parth Shah
2019-10-16 11:51 ` Vincent Guittot
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