Re: CFQ iosched praise: good perfomance and better latency

[Daniel Pittman <daniel@rimspace.net>]

On Mon, 19 Apr 2004, Nick Piggin wrote:
> Pedro Larroy wrote:
>> Hi
>> I've been trying CFQ ioscheduler in my software raid5 with nice
>> results,
>> I've observed that a latency pattern still exists, just as in the
>> anticipatory ioscheduler, but those spikes are now much lower (from
>> 6ms with AS to 2ms with CFQ as seen in the bottom of
>> http://pedro.larroy.com/devel/iolat/analisys/),
>> plus apps seems to get a fair amount of io so they don't get starved.
>> Seems a good choice for io loaded boxes. Thanks Jens Axboe.
> 
> Although AS isn't at its best when behind raid devices (it should
> probably be in front of them), you could be seeing some problem
> with the raid code.

Hrm.  So, if AS isn't a good to have behind RAID devices, but is
reasonable before them, is there any easy way to configure a system like
that?

I don't see an easy way to change the IO scheduler on a per-device basis
anywhere...

        Daniel


-- 
A wonderful discovery, psychoanalysis.  
Makes quite simple people feel they're complex.
        -- S. N. Behrman