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    SubjectRe: Large slowdown with 'x86: Avoid invoking RCU when CPU is idle'
    On Tue, Feb 21, 2012 at 08:16:53PM -0500, Josh Boyer wrote:
    > Hi Paul,
    >
    > Over in Fedora land, I applied your patch from this thread:
    >
    > https://lkml.org/lkml/2012/1/24/441
    >
    > to our 3.3-rc3/rc4 based rawhide kernels. The intention was to solve an
    > RCU issue that was very similar to what Eric originally reported, and
    > the RCU splat did indeed go away[1].
    >
    > However, we then got a few reports of kernels containing that patch
    > being extremely slow. When the patch was dropped, the slowness goes
    > away according to one reporter. The details can be found in this bug:
    >
    > https://bugzilla.redhat.com/show_bug.cgi?id=795050
    >
    > The slowness doesn't seem to hit everyone, and in my local testing
    > things seem to be working just fine. The reporters have widely varying
    > hardware as well, so it doesn't seem machine specific.
    >
    > Perhaps I misdiagnosed the original issue, or perhaps I missed something
    > else that needs to be applied prior to this but I thought I would point
    > this out in case you had any ideas.

    This patch has been obsoleted by patches #45-47 in this series:

    https://lkml.org/lkml/2012/2/3/459

    And patch #47 in that series has been obsoleted by another series
    from Steven Rostedt:

    https://lkml.org/lkml/2012/2/7/231

    Hopefully these fix both splats and slowness.

    Thanx, Paul

    > josh
    >
    > [1] https://bugzilla.redhat.com/show_bug.cgi?id=789641
    >



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