linux-kernel - Documentation on CFQ iosched parameters

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Message-Id: <200809221715.33143.ms@teamix.de>
Date:	Mon, 22 Sep 2008 17:15:26 +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>
Subject: Documentation on CFQ iosched parameters

Please CC to me unless you answer to linux-fsdevel as well. I am not 
subscribed to linux-kernel.

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
slice_async_rq:2
slice_idle:6
slice_sync:100

AFAIR there has been a documentation file somewhere, but I can't find it:

ms@...go> grep -ir "cfq" *   ~/lokal/Kernel/linux-2.6.26/Documentation/block
00-INDEX:       - Block io priorities (in CFQ scheduler)
ioprio.txt:With the introduction of cfq v3 (aka cfq-ts or time sliced cfq), 
basic io
ioprio.txt:with cfq; other io schedulers do not support io priorities thus 
far.
ioprio.txt:CFQ implements three generic scheduling classes that determine how 
io is
switching-sched.txt:'noop', 'as' and 'cfq' (the default) are also available. 
IO schedulers are
switching-sched.txt:for instance, to set the CFQ scheduler for the system 
default, but
switching-sched.txt:noop anticipatory deadline [cfq]
switching-sched.txt:noop [anticipatory] deadline cfq

(unlike as-iosched.txt)

I am willing to write that documentation if someone explain these to me so 
that I understand them ;-).

[1] 
http://www.linux-magazin.de/heft_abo/ausgaben/2005/04/kern_technik/(offset)/4

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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