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    SubjectRe: [PATCH] block: strip out locking optimization in put_io_context()
    Hello,

    On Thu, Feb 09, 2012 at 02:22:32PM +0800, Shaohua Li wrote:
    > >> Tried all the options, the regression still exists. Any new idea?
    > >> I'll spend some time on it if I can get anything
    > >
    > > Can you please try the following one?  Thanks a lot!
    > doesn't work.
    > I also double confirmed b2efa05265d62 causes the regression

    I'll soon send a RCU based version. I'm still having trouble
    reproducing the regression tho. I've tried a few different things.

    * Heavy thrashing: Disk IO dominates everything and CPUs aren't too
    busy. While how swap behaves affects completion time, I don't see
    how CPU locking issue comes into play at all under this
    circumstance.

    * Some swap load: Simulated w/ 1G memory limit and buliding defconfig
    kernel in tmpfs. Swap grows to a couple hundred megabytes but build
    time is still dominated by CPU. I didn't see any meanginful
    difference before and after the commit - both in terms of wallclock
    and CPU times.

    Maybe these two were too extreme to show the problem and I need to
    push memory limit a bit further, but it would be great if you can give
    me a bit more details about your testing.

    * How much memory does the machine have? How is the tmpfs setup and
    filled up? What's the size of the tmpfs and the output of "free -m"
    right before test starts? While the test is running, how occupied
    are the CPUs? On test completion, what's the output of "free -m"?

    * What exactly is the test and what do you measure? What does "12%
    regression" mean? Is it wallclock time or CPU time? If it's CPU
    time, does systime increase dominate the regression?

    Thanks.

    --
    tejun
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