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

From: Viresh Kumar
Date: Tue Jun 18 2013 - 23:00:21 EST

On 19 June 2013 06:50, Xiaoguang Chen <chenxg.marvell@xxxxxxxxx> wrote:
> 2013/6/19 Rafael J. Wysocki <rjw@xxxxxxx>:
>> On Thursday, June 13, 2013 05:01:58 PM Xiaoguang Chen wrote:
>>> cpufreq governor stop and start should be kept in sequence.
>>> If not, there will be unexpected behavior, for example:
>>> we have 4 cpus and policy->cpu=cpu0, cpu1/2/3 are linked to cpu0.
>> Please spell cpus as "CPUs". And please start sequences from capitals.
> Ok, thanks for the remind
>> [Yes, it *really* is a problem.]

Just wanted to know the reasoning behind it so that I can remind
others about it and then argue :)

>>> the normal sequence is as below:
>>> 1) Current governor is userspace, one application tries to set
>>> governor to ondemand. it will call __cpufreq_set_policy in which it
>>> will stop userspace governor and then start ondemand governor.
>> Do I think correctly that this is for all CPUs?
> From current code design, it is for all CPUs.

Why? This can be for a single cpu (which would eventually force all
others CPUs sharing policy with it).
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