linux-kernel - Re: [PATCHSET] blk-throttle: implement proper hierarchy support

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Message-ID: <20130502184953.GP19814@mtj.dyndns.org>
Date:	Thu, 2 May 2013 11:49:53 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: Re: [PATCHSET] blk-throttle: implement proper hierarchy support

Hello,

On Thu, May 02, 2013 at 02:45:14PM -0400, Vivek Goyal wrote:
> I did not understand this point. In flat model, application issuing
> at configured page will not get penalized.
> 
> This penalty is coming from the fact that we are moving bios after the
> wait and make them wait in another queue.
> 
> In flat model there is no such problem. So to me, it is the problem
> of how hierarchical scheduling is implemented. In flat model, I did
> not have to deal with it.

But seen from the parent, the child isn't different from any other
issuer in flat hierarchy.  It's just being repeated, so if you assume
a process which behaves in the exact same manner, that process would
get penalized too.  e.g. imagine an application which throttles itself
and issues exactly 1MB/s amount of data in direct IO.  It'd get
penalized the same way, right?

> Ok. Not having a perfect algorithm now is fine. We can always redo it
> later.

I think we can do source-based RR on bio_lists[] fetching which is
simple enough and should be able to avoid most of the problems, right?

Thanks.

-- 
tejun
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