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From: Jeff Moyer on 13 Jul 2010 09:20
Gui Jianfeng <guijianfeng(a)cn.fujitsu.com> writes:

> It doesn't make sence to store left time slice for an idle workload
> or for the cfqq that uses up its slice.

Did you actually observe any problems? As I understand it, if you
overrun your slice you get a negative offset, so I think we want to keep
that.

Cheers,
Jeff
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From: Jeff Moyer on 14 Jul 2010 09:30
Gui Jianfeng <guijianfeng(a)cn.fujitsu.com> writes:

> Jeff Moyer wrote:
>> Gui Jianfeng <guijianfeng(a)cn.fujitsu.com> writes:
>>
>>> It doesn't make sence to store left time slice for an idle workload
>>> or for the cfqq that uses up its slice.
>>
>> Did you actually observe any problems? As I understand it, if you
>> overrun your slice you get a negative offset, so I think we want to keep
>> that.
>
> Hi Jeff
>
> If that's the case, do we also need to store the negative offset when slice
> used up in cfq_select_queue() and cfq_idle_slice_timer()?

Good question; the code is inconsistent as it stands.

/*
* store what was left of this slice, if the queue idled/timed out
*/

If we are to believe that comment, then yes, we should also call
cfq_slice_expired with timed_out set to 1 in cfq_idle_slice_timer when
the slice is used, and for certain cases in select_queue.

I find this counter-intuitive, actually. I would have stored residual
for quite the opposite situation: where you are preempted and so don't
get to run for your fair share. But, there must be some
logic/experience behind the current mechanism....

Cheers,
Jeff
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