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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 <vgoyal@redhat.com> 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 <jmoyer@redhat.com>
>>> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
>>
>> Hi Jens,
>>
>> Do you have any concerns regarding this patch?
>
> Acked-by: Jeff Moyer <jmoyer@redhat.com>
>
> 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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