[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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 975cdfc..7a8ef0f 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -146,9 +146,9 @@
/* 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 @@
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 @@
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 @@
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 @@
*/
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 @@
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;