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SubjectRe: [PATCH 1/3] cfq-iosched: Implment IOPS mode
Date
Vivek Goyal <vgoyal@redhat.com> writes:

> o Implement another CFQ mode where we charge queue/group in terms of number
> of requests dispatched instead of measuring the time. Measuring in terms
> of time is not possible when we are driving deeper queue depths and there
> are requests from multiple cfq queues in the request queue.
>
> o This mode currently gets activated if one sets slice_idle=0 and associated
> disk supports NCQ. Again the idea is that on an NCQ disk with idling disabled
> most of the queues will dispatch 1 or more requests and then cfq queue
> expiry happens and we don't have a way to measure time. So start providing
> fairness in terms of IOPS.
>
> o Currently this primarily is beneficial with cfq group scheduling where one
> can disable slice idling so that we don't idle on queue and drive deeper
> request queue deptsh (achieving better throughput), at the same time group
> idle is enabled so one should get service differentiation among groups.

I like that this is more isolated now. I'm slowly warming up to it. I
have one question--just a curiosity, really. What do you see now for
the reported sl_used in blktrace when slice_idle is zero and the
hardware supports command queueing?

Cheers,
Jeff


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