cfq-iosched: account for slice over/under time
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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index d44402a..039b38c 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -147,8 +147,8 @@
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 @@
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 @@
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 @@
__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 @@
* 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 @@
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);
@@ -1586,11 +1586,6 @@
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 @@
{
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.