From: Valentin Schneider <valentin.schneider@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>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Quentin Perret <quentin.perret@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>
Subject: Re: [PATCH v2 4/8] sched/fair: rework load_balance
Date: Fri, 30 Aug 2019 15:33:55 +0100 [thread overview]
Message-ID: <6d7bac10-03c4-8825-2e4d-c775b0b88cfb@arm.com> (raw)
In-Reply-To: <CAKfTPtAnHSZ9Lb+JUktA8Z_90V9egzU=M5ErrE=PUGy8qUWLBQ@mail.gmail.com>
On 29/08/2019 15:26, Vincent Guittot wrote:
[...]
>> Seeing how much stuff we already do in just computing the stats, do we
>> really save that much by doing this? I'd expect it to be negligible with
>> modern architectures and all of the OoO/voodoo, but maybe I need a
>> refresher course.
>
> We are not only running on top/latest architecture
>
I know, and I'm not going to argue for a mere division either. I think I
made my point.
[...]>>>>> + if (busiest->group_type == group_misfit_task) {
>>>>> + /* Set imbalance to allow misfit task to be balanced. */
>>>>> + env->balance_type = migrate_misfit;
>>>>> + env->imbalance = busiest->group_misfit_task_load;
>>>>
>>>> AFAICT we don't ever use this value, other than setting it to 0 in
>>>> detach_tasks(), so what we actually set it to doesn't matter (as long as
>>>> it's > 0).
>>>
>>> not yet.
>>> it's only in patch 8/8 that we check if the tasks fits the cpu's
>>> capacity during the detach_tasks
>>>
>>
>> But that doesn't use env->imbalance, right? With that v3 patch it's just
>> the task util's, so AFAICT my comment still stands.
>
> no, misfit case keeps using load and imbalance like the current
> implementation in this patch.
> The modifications on the way to handle misfit task are all in patch 8
>
Right, my reply was a bit too terse. What I meant is that with patch 8 the
value of env->imbalance is irrelevant when dealing with misfit tasks - we
only check the task's utilization in detach_tasks(), we don't do any
comparison of the task's signals with env->imbalance.
Whether we set the imbalance to the load value and set it to 0 in
detach_tasks() or set it to 1 and decrement it in detach_tasks() gives the
same result. That's why I was saying it conceptually fits with the
migrate_task logic, since we can set the imbalance to 1 (we only want to
migrate one task).
next prev parent reply other threads:[~2019-08-30 14:33 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 [this message]
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
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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