linux-kernel - Re: Regarding dm-ioband tests

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Message-Id: <20090910.124547.71116284.ryov@valinux.co.jp>
Date:	Thu, 10 Sep 2009 12:45:47 +0900 (JST)
From:	Ryo Tsuruta <ryov@...inux.co.jp>
To:	vgoyal@...hat.com
Cc:	riel@...hat.com, linux-kernel@...r.kernel.org, dm-devel@...hat.com,
	jens.axboe@...cle.com, agk@...hat.com, akpm@...ux-foundation.org,
	nauman@...gle.com, guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	balbir@...ux.vnet.ibm.com
Subject: Re: Regarding dm-ioband tests

Hi Vivek,

Vivek Goyal <vgoyal@...hat.com> wrote:
> > In addition,
> > there are devices which doesn't use standard IO schedulers, and
> > dm-ioband can work on even such devices.
> 
> This is a interesting use case. Few thoughts.
> 
> - Can't io scheduling mechanism of these devices make use of elevator and
>   elevator fair queuing interfaces to take advantage of io controlling
>   mechanism. It should not be too difficult. Look at noop. It has
>   just 131 lines of code and it now supports hierarchical io scheduling.
>  
>   This will come with request queue and its merging and plug/unplug
>   mechanism. Is that an issue?
>
> - If not, then yes, for these corner cases, io scheduler based controller
>   does not work as it is.

I have a extreme fast SSD and its device driver provides its own
make_request_fn(). So the device driver intercepts IO requests and the
subsequent processes are done within it.

Thanks,
Ryo Tsuruta
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