Re: Control IO related to a process

[MHR <mhullrich@xxxxxxxxx>]

On Tue, Sep 2, 2008 at 9:51 AM, Joseph L. Casale
<JCasale@xxxxxxxxxxxxxxxxx> wrote:
>
> Appreciate that info, I have just been reading about the difference but
> cant say I understand in real life what the difference between deadline
> versus cfq is. I will try changing it on the fly and running my tests.
>

The CFQ elevator algorithm attempts to be fair to all i/o requests,
without specific regard to performance.  The deadline elevator is more
aggressive in scheduling for minimal latency per device.

For example, if you have one process that is doing more or less random
i/o and another that is doing large block sequential i/o, the deadline
elevator will pander to the latter whereas the cfq elevator will try
to be fair in scheduling the i/os between the processes.

Here's a decent, short write up on them:
http://www.redhat.com/magazine/008jun05/features/schedulers/

HTH

mhr
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