linux-kernel - Re: [PATCH v5] cpufreq: fix governor start/stop race condition

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Message-ID: <10398431.HfgFiK9AG8@vostro.rjw.lan>
Date:	Thu, 20 Jun 2013 00:50:44 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Xiaoguang Chen <chenxg.marvell@...il.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Xiaoguang Chen <chenxg@...vell.com>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	njiang1@...vell.com, zjwu@...vell.com, ylmao@...vell.com
Subject: Re: [PATCH v5] cpufreq: fix governor start/stop race condition

On Wednesday, June 19, 2013 11:26:13 AM Xiaoguang Chen wrote:
> 2013/6/19 Viresh Kumar <viresh.kumar@...aro.org>:
> > On 19 June 2013 08:43, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >> On 19 June 2013 06:50, Xiaoguang Chen <chenxg.marvell@...il.com> wrote:
> >>> 2013/6/19 Rafael J. Wysocki <rjw@...k.pl>:
> >>
> >>>>> 2) Current governor is userspace, now cpu0 hotplugs in cpu3, it will
> >>>>
> >>>> Can you please tell me what the above is supposed to mean?  Is it supposed to
> >>>> mean "the online of cpu3 is being run on cpu0" or something different?  If
> >>>> something different, then what?
> 
> Sorry I missed this question, Let me explain it in detail
> Suppose we are in such condtition, current cpufreq goveror is
> userspace governor. cpu3 is offline.
> and two things happen as above two cases, first thing is application
> tries to change current governor to ondemand governor,
> second thing is cpu0 tries to make cpu3 online which is off line
> before. both of these two cases will try to stop current governor and
> start a governor. if above two things interleave, unexpected behavior
> will happen.

Now it's clear, thanks for the explanation.  [Well, I'll still need to fix up
the changelog.  Sigh.]

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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