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    SubjectRe: [PATCH 19/21] cpuidle: create list of registered drivers
    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@linaro.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
    >
    > 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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