Re: Time sliced CFQ io scheduler

Prakash K. Cheemplavam
2004-12-03T10:45:20Z

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Jens Axboe schrieb:
> On Fri, Dec 03 2004, Jens Axboe wrote:
>
>>Funky. It looks like another case of the io scheduler being at the wrong
>>place - if raid sends dependent reads to different drives, it screws up
>>the io scheduling. The right way to fix that would be to io scheduler
>>before raid (reverse of what we do now), but that is a lot of work. A
>>hack would be to try and tie processes to one md component for periods
>>of time, sort of like cfq slicing.
>
>
> It makes sense to split the slice period for sync and async requests,
> since async requests usually get a lot of requests queued in a short
> period of time. Might even make sense to introduce a slice_rq value as
> well, limiting the number of requests queued in a given slice.
>
> But at least this patch lets you set slice_sync and slice_async
> seperately, if you want to experiement.

An idea, which values I should try?

In generell I rather have the impression the problem I am experiencing
is not the problem of the io scheduler alone or why do all show the same
problem?

BTW, I just did my little test on the ide drive and it shows the same
problem, so it is not sata / libata related.

Prakash

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