From: Valdis.Kletnieks@vt.edu
To: Johannes Weiner <jweiner@redhat.com>
Cc: Greg Thelen <gthelen@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Balbir Singh <bsingharora@gmail.com>,
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Subject: Re: [PATCH] memcg: remove unneeded preempt_disable
Date: Thu, 18 Aug 2011 10:26:58 -0400 [thread overview]
Message-ID: <96939.1313677618@turing-police.cc.vt.edu> (raw)
In-Reply-To: Your message of "Thu, 18 Aug 2011 11:38:00 +0200." <20110818093800.GA2268@redhat.com>
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On Thu, 18 Aug 2011 11:38:00 +0200, Johannes Weiner said:
> Note that on non-x86, these operations themselves actually disable and
> reenable preemption each time, so you trade a pair of add and sub on
> x86
>
> - preempt_disable()
> __this_cpu_xxx()
> __this_cpu_yyy()
> - preempt_enable()
>
> with
>
> preempt_disable()
> __this_cpu_xxx()
> + preempt_enable()
> + preempt_disable()
> __this_cpu_yyy()
> preempt_enable()
>
> everywhere else.
That would be an unexpected race condition on non-x86, if you expected _xxx and
_yyy to be done together without a preempt between them. Would take mere
mortals forever to figure that one out. :)
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next prev parent reply other threads:[~2011-08-18 14:27 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-18 6:50 Greg Thelen
2011-08-18 6:52 ` KAMEZAWA Hiroyuki
2011-08-18 9:38 ` Johannes Weiner
2011-08-18 14:26 ` Valdis.Kletnieks [this message]
2011-08-18 14:41 ` Johannes Weiner
2011-08-18 18:27 ` Valdis.Kletnieks
2011-08-18 21:40 ` Andrew Morton
2011-08-19 0:00 ` Greg Thelen
2011-08-25 14:57 ` Peter Zijlstra
2011-08-25 15:11 ` Christoph Lameter
2011-08-25 16:20 ` James Bottomley
2011-08-25 16:31 ` Christoph Lameter
2011-08-25 16:34 ` James Bottomley
2011-08-25 17:07 ` Christoph Lameter
2011-08-25 18:34 ` James Bottomley
2011-08-25 18:46 ` Christoph Lameter
2011-08-25 18:49 ` Peter Zijlstra
2011-08-25 18:53 ` Peter Zijlstra
2011-08-25 19:05 ` Peter Zijlstra
2011-08-25 19:19 ` Christoph Lameter
2011-08-25 22:56 ` Peter Zijlstra
2011-08-25 19:29 ` James Bottomley
2011-08-25 23:01 ` Peter Zijlstra
2011-08-25 18:40 ` Peter Zijlstra
2011-09-06 9:58 ` Johannes Weiner
2011-09-06 10:04 ` KAMEZAWA Hiroyuki
2011-09-06 10:49 ` Johannes Weiner
2011-09-06 10:45 ` KAMEZAWA Hiroyuki
2011-09-06 18:04 ` Greg Thelen
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