linux-kernel - Re: [PATCH] cpufreq: create per policy rwsem instead of per cpu cpu_policy

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Date:	Wed, 18 Sep 2013 13:31:26 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	"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>
Subject: Re: [PATCH] cpufreq: create per policy rwsem instead of per cpu cpu_policy_rwsem

On 18 September 2013 12:39, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> On 09/17/2013 09:20 PM, Viresh Kumar wrote:

> The code looks good, but the patch doesn't apply properly, because of the code
> change that went in in your patch "cpufreq: Clear policy->cpus bits in
> __cpufreq_remove_dev_finish()".

Hmm.. Because of the number of patches floating now a days, it is getting more
and more complex..

I will sort things out once Rafael starts picking stuff for 3.13..

>> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h

>> +     /*
>> +      * The rules for this semaphore:
>> +      * - Any routine that wants to read from the policy structure will
>> +      *   do a down_read on this semaphore.
>> +      * - Any routine that will write to the policy structure and/or may take away
>> +      *   the policy altogether (eg. CPU hotplug), will hold this lock in write
>> +      *   mode before doing so.
>> +      *
>> +      * Additional rules:
>> +      * - Governor routines that can be called in cpufreq hotplug path should not
>> +      *   take this sem as top level hotplug notifier handler takes this.
>
> I think this comment is obsolete. I don't see the top-level hotplug notifier handler
> (cpufreq_cpu_callback) acquiring the rwsem. Good to fix this comment while we are
> at it, perhaps in a separate patch. (The comment above __cpufreq_remove_dev about
> the policy-rwsem appears to be similarly out of date).

Yeah.. Will get that done, but will send these again only once Rafael is picking
stuff for 3.13..
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