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

[Daniel Lezcano]

On 09/28/2013 11:33 PM, Paul E. McKenney wrote:
> On Thu, Sep 26, 2013 at 10:19:14AM +0200, Daniel Lezcano wrote:
> > On 09/26/2013 08:17 AM, Viresh Kumar wrote:
> > > On 26 September 2013 04:00, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> 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
>
> But you should be able to use SRCU in the idle path, if that helps.

Interesting, thanks for the pointer.

  -- Daniel


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