From: Valentin Schneider <valentin.schneider@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de, mingo@kernel.org,
linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
qais.yousef@arm.com, swood@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, vincent.donnefort@arm.com, tj@kernel.org
Subject: Re: [PATCH -v2 15/17] sched: Fix migrate_disable() vs rt/dl balancing
Date: Tue, 06 Oct 2020 17:19:43 +0100 [thread overview]
Message-ID: <jhjr1qbmin4.mognet@arm.com> (raw)
In-Reply-To: <20201006134850.GV2628@hirez.programming.kicks-ass.net>
On 06/10/20 14:48, Peter Zijlstra wrote:
> On Tue, Oct 06, 2020 at 12:20:43PM +0100, Valentin Schneider wrote:
>>
>> An alternative I could see would be to prevent those piles from forming
>> altogether, say by issuing a similar push_cpu_stop() on migrate_disable()
>> if the next pushable task is already migrate_disable(); but that's a
>> proactive approach whereas yours is reactive, so I'm pretty sure that's
>> bound to perform worse.
>
> I think it is always possible to form pileups. Just start enough tasks
> such that newer, higher priority, tasks have to preempt existing tasks.
>
> Also, we might not be able to place the task elsewhere, suppose we have
> all our M CPUs filled with an RT task, then when the lowest priority
> task has migrate_disable(), wake the highest priority task.
>
> Per the SMP invariant, this new highest priority task must preempt the
> lowest priority task currently running, otherwise we would not be
> running the M highest prio tasks.
>
Right, and it goes the other way around for the migrate_disable() task: if
it becomes one of the M highest prio tasks, then it *must* run, and
push/pulling its CPU's current away is the only way to do so...
> That's not to say it might not still be beneficial from trying to avoid
> them, but we must assume a pilup will occur, therefore my focus was on
> dealing with them as best we can first.
"Funny" all that... Thanks!
next prev parent reply other threads:[~2020-10-06 16:19 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-05 14:57 [PATCH -v2 00/17] sched: Migrate disable support Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 01/17] stop_machine: Add function and caller debug info Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 02/17] sched: Fix balance_callback() Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 03/17] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Peter Zijlstra
2020-10-06 7:25 ` Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 04/17] sched/core: Wait for tasks being pushed away on hotplug Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 05/17] workqueue: Manually break affinity " Peter Zijlstra
2020-10-05 16:31 ` Tejun Heo
2020-10-05 14:57 ` [PATCH -v2 06/17] sched/hotplug: Consolidate task migration on CPU unplug Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 07/17] sched: Fix hotplug vs CPU bandwidth control Peter Zijlstra
2020-10-06 12:46 ` Vincent Guittot
2020-10-06 13:33 ` Peter Zijlstra
2020-10-09 20:41 ` Dietmar Eggemann
2020-10-12 12:52 ` Peter Zijlstra
2020-10-12 13:18 ` Peter Zijlstra
2020-10-12 14:14 ` Dietmar Eggemann
2020-10-05 14:57 ` [PATCH -v2 08/17] sched: Massage set_cpus_allowed() Peter Zijlstra
2020-10-06 11:20 ` Valentin Schneider
2020-10-05 14:57 ` [PATCH -v2 09/17] sched: Add migrate_disable() Peter Zijlstra
2020-10-06 11:20 ` Valentin Schneider
2020-10-05 14:57 ` [PATCH -v2 10/17] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() Peter Zijlstra
[not found] ` <CH2PR14MB41833F828B4D3BA5A7B6CE7B9A0B0@CH2PR14MB4183.namprd14.prod.outlook.com>
2020-10-12 11:36 ` Peter Zijlstra
[not found] ` <CH2PR14MB4183BF26F02A4AD4F45CADA59A070@CH2PR14MB4183.namprd14.prod.outlook.com>
2020-10-13 13:20 ` Valentin Schneider
2020-10-05 14:57 ` [PATCH -v2 11/17] sched/core: Make migrate disable and CPU hotplug cooperative Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 12/17] sched,rt: Use cpumask_any*_distribute() Peter Zijlstra
2020-10-06 14:09 ` Juri Lelli
2020-10-06 14:20 ` Peter Zijlstra
2020-10-06 15:55 ` Qais Yousef
2020-10-07 7:22 ` Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 13/17] sched,rt: Use the full cpumask for balancing Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 14/17] sched, lockdep: Annotate ->pi_lock recursion Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 15/17] sched: Fix migrate_disable() vs rt/dl balancing Peter Zijlstra
2020-10-06 7:59 ` Peter Zijlstra
2020-10-06 13:44 ` Steven Rostedt
2020-10-06 13:50 ` Peter Zijlstra
2020-10-06 11:20 ` Valentin Schneider
2020-10-06 13:48 ` Peter Zijlstra
2020-10-06 14:37 ` Juri Lelli
2020-10-06 14:48 ` Peter Zijlstra
2020-10-07 5:29 ` Juri Lelli
2020-10-06 16:19 ` Valentin Schneider [this message]
2020-10-07 19:22 ` Valentin Schneider
2020-10-07 21:08 ` Peter Zijlstra
2020-10-07 22:32 ` Valentin Schneider
2020-10-08 10:48 ` Sebastian Andrzej Siewior
2020-10-12 9:56 ` Dietmar Eggemann
2020-10-12 11:28 ` Peter Zijlstra
2020-10-12 12:22 ` Dietmar Eggemann
2020-10-05 14:57 ` [PATCH -v2 16/17] sched/proc: Print accurate cpumask vs migrate_disable() Peter Zijlstra
2020-10-05 14:57 ` [PATCH -v2 17/17] sched: Add migrate_disable() tracepoints Peter Zijlstra
2020-10-13 14:01 ` [PATCH 1/2] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable() Valentin Schneider
2020-10-13 14:15 ` Sebastian Andrzej Siewior
2020-10-13 14:21 ` Peter Zijlstra
2020-10-15 9:14 ` Valentin Schneider
2020-10-13 14:22 ` Valentin Schneider
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2020-10-13 14:01 ` [PATCH 2/2] sched: Comment affine_move_task() Valentin Schneider
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
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