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    SubjectRe: Question about usage of RCU in the input layer
    On Sat, 21 Mar 2009 22:18:22 -0700
    "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

    > > I'm measuring the time that the following code takes:
    > >
    > > init_completion(&rcu.completion);
    > > /* Will wake me after RCU finished. */
    > > call_rcu(&rcu.head, wakeme_after_rcu);
    > > /* Wait for it. */
    > > wait_for_completion(&rcu.completion);
    > >

    >
    > No, my confusion -- I misread as 2700 milliseconds rather than 2700
    > -microseconds-. 2700 microseconds (or 2.7 milliseconds) is in the
    > expected range for synchronize_rcu() on an HZ=1000 system. 2.7
    > seconds would of course be way out of line.

    > > > If the former, exactly which kernel are you using? The single-CPU
    > > > optimization was added in 2.6.29-rc7, commit ID a682604838.
    > >
    > > a bit after -rc8, specifically commit
    > > 5bee17f18b595937e6beafeee5197868a3f74a06
    >
    > How many synchronize_rcu() calls are you seeing on the boot path?

    I see 20 that hit the above code path (eg ones that wait) until
    userspace starts.


    > Also, are you running with NO_HZ=y?

    of course... is there any other way ? ;-)

    --
    Arjan van de Ven Intel Open Source Technology Centre
    For development, discussion and tips for power savings,
    visit http://www.lesswatts.org


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