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[PATCH] cfq-iosched: use last service point as the fairness criteria 

Right now we use slice_start, which gives async queues an unfair
advantage. Chance that to service_last, and base the resorter
on that.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2007-02-05 11:56:25 +01:00 committed by Jens Axboe
parent b0b8d74941
commit 99f9628aba
1 changed files with 34 additions and 14 deletions
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48
block/cfq-iosched.c
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@ -146,9 +146,9 @@ struct cfq_queue {
/* fifo list of requests in sort_list */
struct list_head fifo;
unsigned long slice_start;
unsigned long slice_end;
unsigned long slice_left;
unsigned long service_last;
/* number of requests that are on the dispatch list */
int on_dispatch[2];
@ -355,7 +355,8 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
{
struct cfq_data *cfqd = cfqq->cfqd;
struct list_head *list;
struct list_head *list, *n;
struct cfq_queue *__cfqq;
/*
* Resorting requires the cfqq to be on the RR list already.
@ -383,15 +384,13 @@ static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
list = &cfqd->rr_list[cfqq->ioprio];
}
/*
* If this queue was preempted or is new (never been serviced), let
* it be added first for fairness but beind other new queues.
* Otherwise, just add to the back of the list.
*/
if (preempted || cfq_cfqq_queue_new(cfqq)) {
struct list_head *n = list;
struct cfq_queue *__cfqq;
/*
* If this queue was preempted or is new (never been serviced),
* let it be added first for fairness but beind other new
* queues.
*/
n = list;
while (n->next != list) {
__cfqq = list_entry_cfqq(n->next);
if (!cfq_cfqq_queue_new(__cfqq))
@ -399,11 +398,32 @@ static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
n = n->next;
}
list_add_tail(&cfqq->cfq_list, n);
} else if (!cfq_cfqq_class_sync(cfqq)) {
/*
* async queue always goes to the end. this wont be overly
* unfair to writes, as the sort of the sync queue wont be
* allowed to pass the async queue again.
*/
list_add_tail(&cfqq->cfq_list, list);
} else {
/*
* sort by last service, but don't cross a new or async
* queue. we don't cross a new queue because it hasn't been
* service before, and we don't cross an async queue because
* it gets added to the end on expire.
*/
n = list;
while ((n = n->prev) != list) {
struct cfq_queue *__cfqq = list_entry_cfqq(n);
list = n;
if (!cfq_cfqq_class_sync(cfqq) || !__cfqq->service_last)
break;
if (time_before(__cfqq->service_last, cfqq->service_last))
break;
}
list_add(&cfqq->cfq_list, n);
}
list_add_tail(&cfqq->cfq_list, list);
}
/*
@ -608,7 +628,6 @@ __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
*/
del_timer(&cfqd->idle_class_timer);
cfqq->slice_start = jiffies;
cfqq->slice_end = 0;
cfqq->slice_left = 0;
cfq_clear_cfqq_must_alloc_slice(cfqq);
@ -1688,6 +1707,7 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
WARN_ON(!cfqq->on_dispatch[sync]);
cfqd->rq_in_driver--;
cfqq->on_dispatch[sync]--;
cfqq->service_last = now;
if (!cfq_class_idle(cfqq))
cfqd->last_end_request = now;