linux-kernel - Re: Documentation on CFQ iosched parameters

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Date:	Tue, 23 Sep 2008 13:15:21 +1000
From:	Aaron Carroll <aaronc@...ato.unsw.edu.au>
To:	Martin Steigerwald <ms@...mix.de>
CC:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: Documentation on CFQ iosched parameters

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.

> slice_async_rq:2

The base number of requests per round for asynchronous queues.  Like
slice_async, the actual maximum is a function of slice_async_rq and I/O
priority.

> slice_idle:6

How long to wait for processes to produce more I/O before switching
queues. This is for anticipation of sequential I/O, and more even disk
time distribution for processes doing back to back synchronous I/Os.

> slice_sync:100

Same as slice_async, but for synchronous requests.

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