linux-kernel - Re: [PATCH 09/14] perf ftrace: Add 'record' sub-command

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Message-ID: <518721F4.6050603@gmail.com>
Date:	Sun, 05 May 2013 21:22:28 -0600
From:	David Ahern <dsahern@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 09/14] perf ftrace: Add 'record' sub-command

On 5/5/13 7:57 PM, Namhyung Kim wrote:
> Hi David,
>
> On Fri, 26 Apr 2013 07:44:18 -0600, David Ahern wrote:
>> On 4/25/13 12:24 AM, Namhyung Kim wrote:
>>> But it looks there's a race between cond_wait() and cond_broatcast().
>>> I'll take a look at that.
>>
>> Why not use eventfd or a pipe for the signalling instead?
>
> Thanks for your feedback!
>
> I didn't have an idea of using eventfd for this case.  Does it helpful
> to prevent such a deadlock like this?

I have used it to replace pthread_cond_wait / 
pthread_cond_{signal,broadcast} -- lighter and faster. It was added in 
2.6.27 I believe, so will be available for any system that supports perf 
(record side). For people compiling perf against say RHEL5 (e.g. 
analysis) you will need a check as to whether it exists.

David

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