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cfq-iosched: account for slice over/under time

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If a slice uses less than it is entitled to (or perhaps more), include
that in the decision on how much time to give it the next time it
gets serviced.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2007-01-19 11:56:49 +11:00 committed by Jens Axboe
parent 44f7c16065
commit c5b680f3b7
1 changed files with 12 additions and 20 deletions
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32
block/cfq-iosched.c
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@ -147,8 +147,8 @@ struct cfq_queue {
struct list_head fifo;
unsigned long slice_end;
unsigned long slice_left;
unsigned long service_last;
long slice_resid;
/* number of requests that are on the dispatch list */
int on_dispatch[2];
@ -251,6 +251,14 @@ static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
cfqq->slice_end += cfqq->slice_resid;
/*
* Don't carry over residual for more than one slice, we only want
* to slightly correct the fairness. Carrying over forever would
* easily introduce oscillations.
*/
cfqq->slice_resid = 0;
}
/*
@ -667,7 +675,6 @@ __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
del_timer(&cfqd->idle_class_timer);
cfqq->slice_end = 0;
cfqq->slice_left = 0;
cfq_clear_cfqq_must_alloc_slice(cfqq);
cfq_clear_cfqq_fifo_expire(cfqq);
cfq_mark_cfqq_slice_new(cfqq);
@ -683,8 +690,6 @@ static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
int preempted)
{
unsigned long now = jiffies;
if (cfq_cfqq_wait_request(cfqq))
del_timer(&cfqd->idle_slice_timer);
@ -699,10 +704,8 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
* store what was left of this slice, if the queue idled out
* or was preempted
*/
if (cfq_slice_used(cfqq))
cfqq->slice_left = cfqq->slice_end - now;
else
cfqq->slice_left = 0;
if (!cfq_cfqq_slice_new(cfqq))
cfqq->slice_resid = cfqq->slice_end - jiffies;
cfq_resort_rr_list(cfqq, preempted);
@ -1364,10 +1367,7 @@ retry:
hlist_add_head(&cfqq->cfq_hash, &cfqd->cfq_hash[hashval]);
atomic_set(&cfqq->ref, 0);
cfqq->cfqd = cfqd;
/*
* set ->slice_left to allow preemption for a new process
*/
cfqq->slice_left = 2 * cfqd->cfq_slice_idle;
cfq_mark_cfqq_idle_window(cfqq);
cfq_mark_cfqq_prio_changed(cfqq);
cfq_mark_cfqq_queue_new(cfqq);
@ -1585,11 +1585,6 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
return 1;
if (!cfq_cfqq_wait_request(new_cfqq))
return 0;
/*
* if it doesn't have slice left, forget it
*/
if (new_cfqq->slice_left < cfqd->cfq_slice_idle)
return 0;
/*
* if the new request is sync, but the currently running queue is
* not, let the sync request have priority.
@ -1614,9 +1609,6 @@ static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
cfq_slice_expired(cfqd, 1);
if (!cfqq->slice_left)
cfqq->slice_left = cfq_prio_to_slice(cfqd, cfqq) / 2;
/*
* Put the new queue at the front of the of the current list,
* so we know that it will be selected next.