linux-kernel - Re: [PATCH 19/21] cpuidle: create list of registered drivers

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Message-ID: <5243EE02.9020207@linaro.org>
Date:	Thu, 26 Sep 2013 10:19:14 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 19/21] cpuidle: create list of registered drivers

On 09/26/2013 08:17 AM, Viresh Kumar wrote:
> On 26 September 2013 04:00, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>> If you introduce a list, you will have to introduce a lock to protect
>> it.
>
> I missed it, should have added that :)
>
>> This lock will be in the fast path cpuidle_idle_call with the
>> get_driver function and conforming to the comment: "NOTE: no locks or
>> semaphores should be used here".
>>
>> A lock has been introduced in this function already and the system hangs
>> with 1024 cpus.
>
> Hmm... I see.. I didn't knew about this expectation.. What about a rcu
> read/write lock? As far as I know its too lightweight... Can we have that
> in fast path?

Nope, we can't use rcu in the idle path :)

http://lists.infradead.org/pipermail/linux-arm-kernel/2012-February/083054.html


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