linux-kernel - Re: [PATCH] blkio-throttle: Avoid calling blkiocg_lookup

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Date:	Mon, 31 Jan 2011 20:25:27 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Jeff Moyer <jmoyer@...hat.com>
CC:	Vivek Goyal <vgoyal@...hat.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] blkio-throttle: Avoid calling blkiocg_lookup_group()
 for root group

On 2011-01-31 20:24, Jens Axboe wrote:
> On 2011-01-31 20:20, Jeff Moyer wrote:
>> Vivek Goyal <vgoyal@...hat.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@...hat.com>
>>>> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
>>>
>>> Hi Jens,
>>>
>>> Do you have any concerns regarding this patch?
>>
>> Acked-by: Jeff Moyer <jmoyer@...hat.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!

Just to be clear, it's queued up in for-linus so it will go to 2.6.38 on
the next push. It was updated last week, this is what it has so far:

Sergey Senozhatsky (1):
      loop: queue_lock NULL pointer derefence in blk_throtl_exit

Stephen M. Cameron (1):
      cciss: make cciss_revalidate not loop through CISS_MAX_LUNS volumes unnecessarily.

Tao Ma (1):
      blktrace: Don't output messages if NOTIFY isn't set.

Tracey Dent (2):
      drivers/block/Makefile: replace the use of <module>-objs with <module>-y
      drivers/block/aoe/Makefile: replace the use of <module>-objs with <module>-y

Vivek Goyal (2):
      cfq: rename a function to give it more appropriate name
      blkio-throttle: Avoid calling blkiocg_lookup_group() for root group

 block/blk-throttle.c       |   10 +++++++++-
 block/cfq-iosched.c        |    6 +++---
 drivers/block/Makefile     |    2 +-
 drivers/block/aoe/Makefile |    2 +-
 drivers/block/cciss.c      |    2 +-
 drivers/block/loop.c       |    3 +++
 kernel/trace/blktrace.c    |    7 +++++++
 7 files changed, 25 insertions(+), 7 deletions(-)

-- 
Jens Axboe

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