linux-kernel - Re: [PATCH 1/2] cpufreq: Add governor operation ongoing flag

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Date:	Wed, 14 Aug 2013 13:18:05 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Xiaoguang Chen <chenxg.marvell@...il.com>
Cc:	Xiaoguang Chen <chenxg@...vell.com>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH 1/2] cpufreq: Add governor operation ongoing flag

I am still not sure if I got what you are trying to say, sorry :(

On 14 August 2013 13:06, Xiaoguang Chen <chenxg.marvell@...il.com> wrote:
> Please see below code in __cpufreq_governor function
>
> mutex_lock(&cpufreq_governor_lock);
> if ((!policy->governor_enabled && (event == CPUFREQ_GOV_STOP)) ||
>                             //////////// <1> Here one process A tries
> to stop governor, it finds governor is enabled, so it will pass down.
>    (policy->governor_enabled && (event == CPUFREQ_GOV_START))) {
>                           /////////////<3> Process B tries to start
> governor, it finds enable flag is false, so it can also pass down.

Processes aren't allowed to call START/STOP in random manner. They
must do a STOP first, if it succeeds do a START.

So lets see it this way:

Process A                            Process B
STOP
                                            STOP
                                            START (If STOP passed)
START (If STOP passed)

So, Process B tries to STOP/START after governor is Stopped by A.
Now call to STOP for process B will fail as we are already stopped..

Can you explain with this example the problem you are trying to solve?
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