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From: Sebastian Siewior <bigeasy@linutronix.de>
To: peterz@infradead.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Qais Yousef <qais.yousef@arm.com>, Scott Wood <swood@redhat.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Ingo Molnar <mingo@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Vincent Donnefort <vincent.donnefort@arm.com>
Subject: Re: [patch 09/10] sched/core: Add migrate_disable/enable()
Date: Thu, 17 Sep 2020 16:38:50 +0200	[thread overview]
Message-ID: <20200917143850.25akkvr32ojtwohy@linutronix.de> (raw)
In-Reply-To: <20200917142438.GH1362448@hirez.programming.kicks-ass.net>

On 2020-09-17 16:24:38 [+0200], peterz@infradead.org wrote:
> And if I'm not mistaken, the above migrate_enable() *does* require being
> able to schedule, and our favourite piece of futex:
> 
> 	raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
> 	spin_unlock(q.lock_ptr);
> 
> is broken. Consider that spin_unlock() doing migrate_enable() with a
> pending sched_setaffinity().

There are two instances of the above and only in the futex code and we
have sort of duct tape for that by manually balancing the migrate
counter so that it does not come to this.
But yes, not having to do the manual balance is a plus.

Sebastian

  reply	other threads:[~2020-09-17 14:43 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-17  9:42 [patch 00/10] sched: Migrate disable support for RT Thomas Gleixner
2020-09-17  9:42 ` [patch 01/10] sched: Fix balance_callback() Thomas Gleixner
2020-09-17  9:42 ` [patch 02/10] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Thomas Gleixner
2020-09-17  9:42 ` [patch 03/10] sched/core: Wait for tasks being pushed away on hotplug Thomas Gleixner
2020-09-17  9:42 ` [patch 04/10] sched/hotplug: Consolidate task migration on CPU unplug Thomas Gleixner
2020-09-17  9:42 ` [patch 05/10] sched/core: Split __set_cpus_allowed_ptr() Thomas Gleixner
2020-09-17  9:42 ` [patch 06/10] sched: Add task components for migration control Thomas Gleixner
2020-09-17  9:42 ` [patch 07/10] sched/core: Add mechanism to wait for affinity setting to complete Thomas Gleixner
2020-09-17  9:42 ` [patch 08/10] sched: Add update_migratory() callback to scheduler classes Thomas Gleixner
2020-09-17  9:42 ` [patch 09/10] sched/core: Add migrate_disable/enable() Thomas Gleixner
2020-09-17 14:24   ` peterz
2020-09-17 14:38     ` Sebastian Siewior [this message]
2020-09-17 14:49       ` peterz
2020-09-17 15:13         ` Sebastian Siewior
2020-09-17 15:54           ` peterz
2020-09-17 16:30             ` Sebastian Siewior
2020-09-18  8:22               ` peterz
2020-09-18  8:48                 ` Sebastian Siewior
2020-09-18  7:00     ` Thomas Gleixner
2020-09-18  8:28       ` peterz
2020-09-17  9:42 ` [patch 10/10] sched/core: Make migrate disable and CPU hotplug cooperative Thomas Gleixner

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