All of lore.kernel.org
 help / color / mirror / Atom feed
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 09/17] sched: Add migrate_disable()
Date: Tue, 06 Oct 2020 12:20:27 +0100	[thread overview]
Message-ID: <jhjwo03mwhw.mognet@arm.com> (raw)
In-Reply-To: <20201005150921.859981475@infradead.org>


On 05/10/20 15:57, Peter Zijlstra wrote:
> Add the base migrate_disable() support (under protest).
>
> While migrate_disable() is (currently) required for PREEMPT_RT, it is
> also one of the biggest flaws in the system.
>
> Notably this is just the base implementation, it is broken vs
> sched_setaffinity() and hotplug, both solved in additional patches for
> ease of review.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
[...]
> @@ -2363,7 +2451,7 @@ int select_task_rq(struct task_struct *p
>  {
>       lockdep_assert_held(&p->pi_lock);
>
> -	if (p->nr_cpus_allowed > 1)
> +	if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p))

So dissociating migrate_disable() from p->nr_cpus_allowed unlocks the whole
DL+RT push/pull thingie, but it also means we need to be somewhat careful
regarding checks like the above.

Looking at current p->nr_cpus_allowed readers, it's mostly DL/RT; I was
somewhat afraid CFS load balance would use it but turns out it doesn't. The
only borderline case I see is call_on_cpu(), and even then it would be just a
performance deal rather than a correctness one.

All that to say: it seems fine to me.

>               cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);
>       else
>               cpu = cpumask_any(p->cpus_ptr);

  reply	other threads:[~2020-10-06 11:20 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 [this message]
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
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=jhjwo03mwhw.mognet@arm.com \
    --to=valentin.schneider@arm.com \
    --cc=bigeasy@linutronix.de \
    --cc=bristot@redhat.com \
    --cc=bsegall@google.com \
    --cc=dietmar.eggemann@arm.com \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mgorman@suse.de \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=qais.yousef@arm.com \
    --cc=rostedt@goodmis.org \
    --cc=swood@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=tj@kernel.org \
    --cc=vincent.donnefort@arm.com \
    --cc=vincent.guittot@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.