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

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Date:	Mon, 12 Jul 2010 09:20:04 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	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 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.

(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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