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    SubjectRe: RCU related performance regression in 3.3
    Le 18/04/2012 16:01, Paul E. McKenney a écrit :
    > On Wed, Apr 18, 2012 at 11:37:28AM +0200, Pascal Chapperon wrote:
    >> Mount and umount operations are not slower with RCU_FAST_NO_HZ during
    >> runtime; systemctl start and stop operations are also not slower. In
    >> fact, i couldn't find a single operation slower during runtime with
    >> RCU_FAST_NO_HZ.
    >
    > Your boot-time setup is such that all CPUs are online before the
    > boot-time mount operations take place, right?
    Yes :
    [ 0.242697] Brought up 8 CPUs
    [ 0.242699] Total of 8 processors activated (35118.33 BogoMIPS).

    > Struggling to understand
    > how RCU can tell the difference between post-CPU-bringup boot time
    > and run time...
    >
    systemd is controlling the whole boot process including mount
    operation (apart root filesystem) and as I can see, uses heavily
    sockets to do it (not to mention cpu-affinity). It controls also the
    major part of umount operations. Is it possible that your patch hits
    a systemd bug ?
    What I don't understand is that systemd coexists well with
    RCU_FAST_NO_HZ on a smaller laptop with older and much less powerful
    cpu.
    I'll do further tests on another machine.

    Pascal

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