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

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Message-ID: <CAKohpo=3qFQ+gD+3u__NtZEL4xu51FBN+og+_UE7aTR26XvRng@mail.gmail.com>
Date:	Thu, 26 Sep 2013 11:47:05 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Daniel Lezcano <daniel.lezcano@...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 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?
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