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    SubjectRe: [PATCH] blkio-throttle: Avoid calling blkiocg_lookup_group() for root group
    On 2011-01-31 20:20, Jeff Moyer wrote:
    > Vivek Goyal <> writes:
    >> On Mon, Jan 17, 2011 at 04:56:06PM -0500, Vivek Goyal wrote:
    >>> o Jeff Moyer was doing some testing on a RAM backed disk and
    >>> blkiocg_lookup_group() showed up high overhead after memcpy(). Similarly
    >>> somebody else reported that blkiocg_lookup_group() is eating 6% extra
    >>> cpu. Though looking at the code I can't think why the overhead of
    >>> this function is so high. One thing is that it is called with very high
    >>> frequency (once for every IO).
    >>> o For lot of folks blkio controller will be compiled in but they might
    >>> not have actually created cgroups. Hence optimize the case of root
    >>> cgroup where we can avoid calling blkiocg_lookup_group() if IO is happening
    >>> in root group (common case).
    >>> Reported-by: Jeff Moyer <>
    >>> Signed-off-by: Vivek Goyal <>
    >> Hi Jens,
    >> Do you have any concerns regarding this patch?
    > Acked-by: Jeff Moyer <>
    > Jens, this is a pretty easy performance regression fixup. I think it
    > should be pulled in sooner rather than later. We've also witnessed this
    > slowdown on big performance testing rigs, so it's not just a ramdisk
    > issue.

    Yep, will fold it into 2.6.38, thanks!

    Jens Axboe

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