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From: Andi Kleen <andi@firstfloor.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Andi Kleen <andi@firstfloor.org>,
	Ivo Sieben <meltedpianoman@gmail.com>,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	linux-serial@vger.kernel.org, Alan Cox <alan@linux.intel.com>,
	Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [REPOST] RFC: sched: Prevent wakeup to enter critical section needlessly
Date: Wed, 10 Oct 2012 16:02:49 +0200	[thread overview]
Message-ID: <20121010140249.GX16230@one.firstfloor.org> (raw)
In-Reply-To: <20121009151729.GA3521@redhat.com>

> wait_event:
> 
> 	prepare_to_wait(wq)	// takes wq->lock
> 
> 	if (!CONDITION)
> 		schedule();
> 
> Now,
> 
> 	CONDITION = 1;
> 	wake_up(wq);
> 
> at least need the full mb() before lits_empty().

You're right, but it would probably only matter for inlining with LTO
(if the LTO compiler ever decides to do that)

Without that a call should be always enough barrier in practice.

So yes I would add the mb, but most likely it will not make much
difference. Just make sure to comment it.

-Andi

  reply	other threads:[~2012-10-10 14:02 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-24 13:06 [PATCH] RFC: sched: Prevent wakeup to enter critical section needlessly Ivo Sieben
2012-09-24 13:06 ` Ivo Sieben
2012-10-09 11:30 ` [REPOST] " Ivo Sieben
2012-10-09 11:30   ` Ivo Sieben
2012-10-09 13:37   ` Andi Kleen
2012-10-09 13:37     ` Andi Kleen
2012-10-09 14:15     ` Peter Zijlstra
2012-10-09 15:17       ` Oleg Nesterov
2012-10-10 14:02         ` Andi Kleen [this message]
2012-10-18  8:30           ` [PATCH-v2] " Ivo Sieben
2012-10-18  8:30             ` Ivo Sieben
2012-10-25 10:12             ` [REPOST-v2] " Ivo Sieben
2012-10-25 10:12               ` Ivo Sieben
2012-11-19  7:30               ` Ivo Sieben
2012-11-19  7:30                 ` Ivo Sieben
2012-11-19 10:20                 ` Preeti U Murthy
2012-11-19 15:10                 ` Oleg Nesterov
2012-11-19 15:34                   ` Ivo Sieben
2012-11-19 15:49                     ` Oleg Nesterov
2012-11-21 13:03                       ` Ivo Sieben
2012-11-21 13:47                         ` Alan Cox
2012-11-21 13:58                         ` Oleg Nesterov

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