linux-kernel - Re: [PATCH 5/6 v4] cfq-iosched: CFQ group hierarchical scheduling and use

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Message-ID: <AANLkTinUcSxJZ24NeUwQ_6W4=+atRWX-7G9K5iymuOsz@mail.gmail.com>
Date:	Wed, 16 Feb 2011 09:28:07 -0800
From:	Divyesh Shah <dpshah@...gle.com>
To:	Gui Jianfeng <guijianfeng@...fujitsu.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Chad Talbott <ctalbott@...gle.com>
Subject: Re: [PATCH 5/6 v4] cfq-iosched: CFQ group hierarchical scheduling and
 use_hierarchy interface

On Wed, Feb 16, 2011 at 9:22 AM, Divyesh Shah <dpshah@...gle.com> wrote:
> On Tue, Feb 15, 2011 at 5:44 PM, Gui Jianfeng
> <guijianfeng@...fujitsu.com> wrote:
>> Hmm, it seems memcg aggregating stats in parent group.
>> But do we really need to do that in kernel? I think it's easier to do it in
>> userland, and it makes kernel much simpler.
>>
>
> I would prefer having stats aggregated up the hierarchy. One trick we
> used at Google earlier was to do lazy updates for most stats. So we

Note that this was on ancient version of the blkio controller :). As
Vivek mentioned,
it may be ok to add the hierarchical accounting later.

> would accumulate stats for a given timeslice and at the end of that
> timeslice propagate those counts all the way up to the parent. For
> device info like this, the update can be instantaneous since its not a
> very frequent event. It would also be very useful to distinguish
> between stats for the cgroup itself vs total values accumulated from
> the subtree rooted at that cgroup like memcg does.
>
> --
> Thanks,
> Divyesh
>



-- 
Thanks,
Divyesh
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