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.
next prev parent 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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