CFQ: Don't store left slice when slice used up or for a idle workload

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

---
 block/cfq-iosched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index eb4086f..d985e38 100644
@@ -3418,7 +3418,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
 		 * - when there is a close cooperator
 		 */
 		if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
-			cfq_slice_expired(cfqd, 1);
+			cfq_slice_expired(cfqd, 0);
 		else if (sync && cfqq_empty &&
 			 !cfq_close_cooperator(cfqd, cfqq)) {
 			cfqd->noidle_tree_requires_idle |=

1.5.4.rc3

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

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()?

Thanks
Gui

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