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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,
	ouwen210@hotmail.com
Subject: Re: [PATCH v4 00/19] sched: Migrate disable support
Date: Thu, 29 Oct 2020 19:03:17 +0000	[thread overview]
Message-ID: <jhj361wq2h6.mognet@arm.com> (raw)
In-Reply-To: <20201023101158.088940906@infradead.org>


On 23/10/20 11:11, Peter Zijlstra wrote:
> Hi,
>
> The fourth version of migrate_disable() for PREEMPT_RT.
>
> Two changes since last time:
>
>  - fixes !SMP builds (bigeasy)
>  - TLA+ validation of migrate_disable() vs sched_setaffinity() (valsch)
>
> Esp. that latter resulted in significant changes to patch #10. Huge thanks to
> Valentin.
>

I've been poking at that model some more; there's always going to be some
gap between what is being modelled vs what the code actually does, but
I'm mostly happy with the state it is in now.


So far it's been 1 victim task looping around a Migration-Disabled region
while some other threads fight over changing its affinity. The victim task
can also be preempted by some higher-priority task. I didn't make the
victim task block between Migration-Disabled regions.

Last run was 2 CPUs and 2 affinity-changing threads, I'll try to bump that
a bit but it is already somewhat lengthy to run (~10h).

In terms of what this has been checking
- Forward progress (no process forever blocked on some condition / lock)
- Refcounts always >= 0 (hit a few -1's in earlier versions)
- Affinity is respected
  I've "implemented" that as:

    If 'p' is running on a CPU, then that CPU must be in p->cpus_mask when
      !p->migration_pending && p->pi_lock is not held


I don't think I have much else to add, so feel free to add

  Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

To patches 01-14, 16-17.

The RT side of patch 15 looked fine to me, but I didn't spend much time on
DL. We might still want to steal those .pick_task() from coresched to
implement that XXX in push_cpu_stop(), but AIUI this is more of a
performance thing than a correctness one.

  parent reply	other threads:[~2020-10-29 19:03 UTC|newest]

Thread overview: 81+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-23 10:11 [PATCH v4 00/19] sched: Migrate disable support Peter Zijlstra
2020-10-23 10:11 ` [PATCH v4 01/19] stop_machine: Add function and caller debug info Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 02/19] sched: Fix balance_callback() Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-11-11 20:30     ` Paul Bolle
2020-11-11 20:45       ` Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 03/19] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 04/19] sched/core: Wait for tasks being pushed away on hotplug Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
2020-10-23 10:12 ` [PATCH v4 05/19] workqueue: Manually break affinity " Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 06/19] sched/hotplug: Consolidate task migration on CPU unplug Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
2020-10-23 10:12 ` [PATCH v4 07/19] sched: Fix hotplug vs CPU bandwidth control Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 08/19] sched: Massage set_cpus_allowed() Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 09/19] sched: Add migrate_disable() Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 10/19] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-11-12 16:38   ` [PATCH v4 10/19] " Qian Cai
2020-11-12 17:26     ` Valentin Schneider
2020-11-12 18:01       ` Qian Cai
2020-11-12 19:31         ` Valentin Schneider
2020-11-12 19:41           ` Qian Cai
2020-11-12 20:37           ` Qian Cai
2020-11-12 21:26             ` Valentin Schneider
2020-11-13 10:27           ` Peter Zijlstra
2020-11-12 18:35       ` Qian Cai
2020-11-20 12:34     ` [tip: sched/core] sched/core: Add missing completion for affine_move_task() waiters tip-bot2 for Valentin Schneider
2020-10-23 10:12 ` [PATCH v4 11/19] sched/core: Make migrate disable and CPU hotplug cooperative Peter Zijlstra
2020-10-29 16:27   ` Valentin Schneider
2020-10-29 17:34     ` Peter Zijlstra
2020-10-29 17:55       ` Valentin Schneider
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
2020-11-13 15:06   ` [PATCH v4 11/19] " Qian Cai
2020-11-17 19:28     ` Valentin Schneider
2020-11-18 14:44       ` Qian Cai
2020-11-23 18:13         ` Sebastian Andrzej Siewior
2020-12-02 21:59           ` Qian Cai
2020-12-03 12:31           ` Qian Cai
2020-12-04  0:23       ` Qian Cai
2020-12-04 21:19       ` Qian Cai
2020-12-05 18:37         ` Valentin Schneider
2020-12-06  1:17           ` Qian Cai
2020-12-07 19:27         ` Valentin Schneider
2020-12-08 13:46           ` Qian Cai
2020-12-09 19:16             ` Valentin Schneider
2020-10-23 10:12 ` [PATCH v4 12/19] sched,rt: Use cpumask_any*_distribute() Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 13/19] sched,rt: Use the full cpumask for balancing Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 14/19] sched, lockdep: Annotate ->pi_lock recursion Peter Zijlstra
2020-10-29 16:27   ` Valentin Schneider
2020-10-29 17:38     ` Peter Zijlstra
2020-10-29 18:09       ` Valentin Schneider
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 15/19] sched: Fix migrate_disable() vs rt/dl balancing Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-12-26 13:54   ` [PATCH v4 15/19] " Qais Yousef
2021-03-05 14:56     ` Peter Zijlstra
2021-03-05 15:41       ` Valentin Schneider
2021-03-05 17:11         ` Qais Yousef
2021-03-10 14:44         ` Qais Yousef
2021-03-05 16:48       ` Qais Yousef
2020-10-23 10:12 ` [PATCH v4 16/19] sched/proc: Print accurate cpumask vs migrate_disable() Peter Zijlstra
2020-11-11  8:23   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 17/19] sched: Add migrate_disable() tracepoints Peter Zijlstra
2020-10-29 16:27   ` Valentin Schneider
2020-10-29 17:43     ` Peter Zijlstra
2020-10-29 17:56       ` Valentin Schneider
2020-10-29 17:59         ` Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 18/19] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable() Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 19/19] sched: Comment affine_move_task() Peter Zijlstra
2020-10-29 16:27   ` Valentin Schneider
2020-10-29 17:44     ` Peter Zijlstra
2020-10-29 19:03 ` Valentin Schneider [this message]
2020-11-09 16:39 ` [PATCH v4 00/19] sched: Migrate disable support Daniel Bristot de Oliveira

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