linux-kernel - Re: [RFC][PATCH 00/11] blkiocg async support

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Message-ID: <AANLkTin9TCziHU-AX42aVWpaFDX5=4NwojGxFSFnRFAq@mail.gmail.com>
Date:	Thu, 22 Jul 2010 12:28:50 -0700
From:	Greg Thelen <gthelen@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	Nauman Rafique <nauman@...gle.com>,
	Munehiro Ikeda <m-ikeda@...jp.nec.com>,
	linux-kernel@...r.kernel.org, Ryo Tsuruta <ryov@...inux.co.jp>,
	taka@...inux.co.jp, Andrea Righi <righi.andrea@...il.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	akpm@...ux-foundation.org, balbir@...ux.vnet.ibm.com
Subject: Re: [RFC][PATCH 00/11] blkiocg async support

On Sun, Jul 11, 2010 at 5:20 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Sat, 10 Jul 2010 09:24:17 -0400
> Vivek Goyal <vgoyal@...hat.com> wrote:
>
>> On Fri, Jul 09, 2010 at 05:55:23PM -0700, Nauman Rafique wrote:
>>
>> [..]
>> > > Well, right.  I agree.
>> > > But I think we can work parallel.  I will try to struggle on both.
>> >
>> > IMHO, we have a classic chicken and egg problem here. We should try to
>> > merge pieces as they become available. If we get to agree on patches
>> > that do async IO tracking for IO controller, we should go ahead with
>> > them instead of trying to wait for per cgroup dirty ratios.
>> >
>> > In terms of getting numbers, we have been using patches that add per
>> > cpuset dirty ratios on top of NUMA_EMU, and we get good
>> > differentiation between buffered writes as well as buffered writes vs.
>> > reads.
>> >
>> > It is really obvious that as long as flusher threads ,etc are not
>> > cgroup aware, differentiation for buffered writes would not be perfect
>> > in all cases, but this is a step in the right direction and we should
>> > go for it.
>>
>> Working parallel on two separate pieces is fine. But pushing second piece
>> in first does not make much sense to me because second piece does not work
>> if first piece is not in. There is no way to test it. What's the point of
>> pushing a code in kernel which only compiles but does not achieve intented
>> purposes because some other pieces are missing.
>>
>> Per cgroup dirty ratio is a little hard problem and few attempts have
>> already been made at it. IMHO, we need to first work on that piece and
>> get it inside the kernel and then work on IO tracking patches. Lets
>> fix the hard problem first that is necessary to make second set of patches
>> work.
>>
>
> I've just waited for dirty-ratio patches because I know someone is working on.
> But, hmm, I'll consider to start work by myself.

I have some patches that I have to address the dirty-ratios.  I will post them.

These dirty-ratio patches do not do anything intelligent wrt to
per-cgroup writeback.  When a cgroup dirty ratio is exceeded, a
per-bdi writeback is triggered.

> (Off-topic)
> BTW, why io-cgroup's hierarchy level is limited to 2 ?
> Because of that limitation, libvirt can't work well...
>
> Thanks,
> -Kame
>
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