Messages in this thread | | | Date | Tue, 23 Sep 2008 11:32:18 +0200 | From | Jens Axboe <> | Subject | Re: Documentation on CFQ iosched parameters |
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On Tue, Sep 23 2008, Martin Steigerwald wrote: > 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?
That would be great!
> 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/
You can mention the links for v1 and v2, but as they have even little historic relevance, don't spend more time on that.
> - 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?
Yes
> 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?
Even the very first CFQ posted used per-process queues, so there's really very little inheritance from SFQ at all. So I don't think it's particularly interesting to mention. But if you want, go ahead :-)
-- Jens Axboe
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