linux-kernel - Re: Documentation on CFQ iosched parameters

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Date:	Tue, 23 Sep 2008 11:26:51 +0200
From:	Martin Steigerwald <ms@...mix.de>
To:	linux-kernel@...r.kernel.org
Cc:	linux-fsdevel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>,
	Aaron Carroll <aaronc@...ato.unsw.edu.au>
Subject: Re: Documentation on CFQ iosched parameters

Am Dienstag, 23. September 2008 schrieb Aaron Carroll:
> Martin Steigerwald wrote:
> > Hi!
> >
> > I am searching documentation about CFQ io scheduler. I can't find it in
> > linux 2.6.26 Documentation directory.
> >
> > I found about these in german[1]:
> >
> > back_seek_max:16384
> > back_seek_penalty:2
> > fifo_expire_async:250
> > fifo_expire_sync:123
> > quantum:4
> >
> > But I am completely missing about these:
> >
> > slice_async:40
>
> Base length of an asynchronous queue timeslice (that is, how long the
> queue has to dispatch requests each round).  The actual timeslice
> length is scaled by the I/O priority.

[...]

Thanks. As I do not find documentation about CFQ at all, I think I need to 
create a new file from scratch... how about 
Documentation/block/cfq-iosched.txt?

For that I need some more information about CFQ. I found the following 
resources:

- CFQ V3 aka CFQ TS: http://lwn.net/Articles/143474/, 
http://lwn.net/Articles/114770/ and posts by Jens, 
http://lwn.net/Articles/113869/

- CFQ V2: Post by Jens, http://lwn.net/Articles/101029/

- CFQ: Post by Jens, http://lwn.net/Articles/22429/

- Documentation/block/as-iosched.txt / deadline-iosched.txt (as for how an IO 
scheduler can be documented)

Would that be what I should read in order to write such an documentation? 

How about the relevance of CFQ and CFQ v2 stuff? What of it would be good to 
mention? I would like to limit documentation to what is still relevant for 
the current implementation of the IO scheduler. Should I mention its 
inheritance from SFQ - maybe in a small introduction and historic overview?

Ciao,
-- 
Martin Steigerwald - team(ix) GmbH - http://www.teamix.de
gpg: 19E3 8D42 896F D004 08AC A0CA 1E10 C593 0399 AE90

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