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From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: mingo@kernel.org, tglx@linutronix.de,
	linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	frederic@kernel.org, Will Deacon <will@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	npiggin@gmail.com
Subject: Re: [PATCH 0/6] sched: TTWU, IPI, and assorted stuff
Date: Fri, 19 Jun 2020 20:11:28 +0200	[thread overview]
Message-ID: <20200619181128.GC576888@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200619174802.GA10403@paulmck-ThinkPad-P72>

On Fri, Jun 19, 2020 at 10:48:02AM -0700, Paul E. McKenney wrote:
> On Fri, Jun 19, 2020 at 10:20:47AM -0700, Paul E. McKenney wrote:

> > > @@ -2615,7 +2617,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
> > >  	 * let the waker make forward progress. This is safe because IRQs are
> > >  	 * disabled and the IPI will deliver after on_cpu is cleared.
> > >  	 */
> > > -	if (READ_ONCE(p->on_cpu) && ttwu_queue_wakelist(p, cpu, wake_flags | WF_ON_RQ))
> > > +	if (smp_load_acquire(&p->on_cpu) &&
> 
> Given the x86 memory model, this only protects against the compiler
> reordering accesses in ttwu_queue_wakelist() against the fetch of
> p->on_cpu, correct?

Yes.

> Don't get me wrong, I do see some potential compiler misorderings,
> including with cpu_rq(cpu)->nr_running.  Just curious.

Given this is arch independent code, I'd better write generic code, and
there I really think this wants to be acquire. I'll also try and write a
comment for next time.


  reply	other threads:[~2020-06-19 18:11 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-15 12:56 [PATCH 0/6] sched: TTWU, IPI, and assorted stuff Peter Zijlstra
2020-06-15 12:56 ` [PATCH 1/6] sched: Fix ttwu_queue_cond() Peter Zijlstra
2020-06-15 13:34   ` Peter Zijlstra
2020-06-15 16:45     ` Paul E. McKenney
2020-06-15 22:58       ` Paul E. McKenney
2020-06-22  9:11   ` Mel Gorman
2020-06-22  9:41     ` Peter Zijlstra
2020-06-15 12:56 ` [PATCH 2/6] sched: Verify some SMP assumptions Peter Zijlstra
2020-06-15 12:56 ` [PATCH 3/6] sched: s/WF_ON_RQ/WQ_ON_CPU/ Peter Zijlstra
2020-06-22  9:13   ` Mel Gorman
2020-06-15 12:56 ` [PATCH 4/6] smp, irq_work: Continue smp_call_function*() and irq_work*() integration Peter Zijlstra
2020-06-15 12:56 ` [PATCH 5/6] irq_work: Cleanup Peter Zijlstra
2020-06-16 15:16   ` Petr Mladek
2020-06-15 12:57 ` [PATCH 6/6] smp: Cleanup smp_call_function*() Peter Zijlstra
2020-06-15 14:34   ` Jens Axboe
2020-06-15 16:04   ` Daniel Thompson
2020-06-17  8:23   ` Christoph Hellwig
2020-06-17  9:00     ` Peter Zijlstra
2020-06-17 11:04     ` Peter Zijlstra
2020-06-18  6:51       ` Christoph Hellwig
2020-06-18 16:25         ` Peter Zijlstra
2020-06-15 16:23 ` [PATCH 0/6] sched: TTWU, IPI, and assorted stuff Paul E. McKenney
2020-06-15 16:40   ` Peter Zijlstra
2020-06-15 17:21     ` Paul E. McKenney
2020-06-15 19:11       ` Peter Zijlstra
2020-06-15 19:55         ` Paul E. McKenney
2020-06-16 16:31           ` Paul E. McKenney
2020-06-16 17:04         ` Peter Zijlstra
2020-06-16 17:17           ` Peter Zijlstra
2020-06-16 17:53             ` Paul E. McKenney
2020-06-19 13:44             ` Peter Zijlstra
2020-06-19 17:20               ` Paul E. McKenney
2020-06-19 17:48                 ` Paul E. McKenney
2020-06-19 18:11                   ` Peter Zijlstra [this message]
2020-06-19 18:46                     ` Paul E. McKenney
2020-06-20 18:46               ` Paul E. McKenney
2020-06-16 17:51           ` Paul E. McKenney

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