linux-kernel - Re: [PATCH] io-controller: implement per group request allocation limitation

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Date:	Tue, 04 Aug 2009 14:38:35 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Munehiro Ikeda <m-ikeda@...jp.nec.com>
CC:	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	jens.axboe@...cle.com, nauman@...gle.com, dpshah@...gle.com,
	lizf@...fujitsu.com, mikew@...gle.com, fchecconi@...il.com,
	paolo.valente@...more.it, ryov@...inux.co.jp,
	fernando@....ntt.co.jp, s-uchida@...jp.nec.com, taka@...inux.co.jp,
	jmoyer@...hat.com, dhaval@...ux.vnet.ibm.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	jbaron@...hat.com, agk@...hat.com, snitzer@...hat.com,
	akpm@...ux-foundation.org, peterz@...radead.org
Subject: Re: [PATCH] io-controller: implement per group request allocation
 limitation

Munehiro Ikeda wrote:
...
> 
> Consideration and Conclusion
> =============================
> 
>  From result(1), it is observed that it takes 1000~1200[ms] to rise P2
> bandwidth.  In result(2), where both of g1 and g2 have
> nr_group_requests=100, the delay gets longer as 1800~2000[ms].  In
> addition to it, the average bandwidth becomes ~5% lower than result(1). 
> This is supposed that P2 couldn't allocate enough requests.
> Then, result(3) shows that bandwidth of P2 can rise quickly (~300[ms])
> if nr_group_requests can be set per-cgroup.  Result(4) shows that the
> delay can be shortened by setting g2 as RT class, however, the delay is
> still longer than result(3).
> 
> I think it is confirmed that "per-cgroup nr_requests limitation is
> useful in a certain situation".  Beyond that, the discussion topic is
> the benefit pointed out above is eligible for the complication of the
> implementation.  IMHO, I don't think the implementation of per-cgroup
> request limitation is too complicated to accept.  On the other hand I
> guess it suddenly gets complicated if we try to implement further more,
> especially hierarchical support.  It is also true that I have a feeling
> that implementation without per-device limitation and hierarchical
> support is like "unfinished work".
> 
> So, my opinion so far is that, per-cgroup nr_requests limitation should
> be merged only if hierarchical support is concluded "unnecessary" for
> it.  If merging it tempts hierarchical support, it shouldn't be.
> How about your opinion, all?

  Hi Munehiro-san,

  Thanks for the great job. It seems Per-cgroup requests allocation limits
  has its value in some cases. IMHO, for the time being, we can just drop
  the hierarchical support for "Per-cgroup requests allocation limits", and
  see whether it can work well.

> 
> My considerations or verification method might be wrong.  Please correct
> them if any.  And if you have any other idea of scenario to verify the
> effect of per-cgroup nr_requests limitation, please let me know.  I'll
> try it.
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 

-- 
Regards
Gui Jianfeng

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