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    SubjectRe: Large slowdown with 'x86: Avoid invoking RCU when CPU is idle'
    On Tue, Feb 21, 2012 at 05:32:52PM -0800, Paul E. McKenney wrote:
    > 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.

    First off, thanks for the quick reply!

    > This patch has been obsoleted by patches #45-47 in this series:
    >
    > https://lkml.org/lkml/2012/2/3/459

    Holy lots of patches...

    > And patch #47 in that series has been obsoleted by another series
    > from Steven Rostedt:
    >
    > https://lkml.org/lkml/2012/2/7/231

    Ok.

    > Hopefully these fix both splats and slowness.

    So again, I'm slightly confused on how RCU patches flow. Eric
    originally reported the bug for which you created the patch I applied
    against 3.3. The giant patch series above seems queued for 3.4.

    I don't see stable CC'd on 45-47, nor any of Steven's patches. I doubt
    I'd want to go applying the 47-patch series on 3.3 at the moment, and
    given you have these marked for 3.4 I don't think you do either.
    However, is there some kind of fix for the original bug report against
    3.3?

    josh


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