cfq-iosched: improve preemption for cooperating tasks
When testing the syslet async io approach, I discovered that CFQ
sometimes didn't perform as well as expected. cfq_should_preempt()
needs to better check for cooperating tasks, so fix that by allowing
preemption of an equal priority queue if the recently queued request
is as good a candidate for IO as the one we are currently waiting for.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f92ba2a..bfb3967 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -867,15 +867,11 @@
static void cfq_dispatch_insert(request_queue_t *q, struct request *rq)
{
- struct cfq_data *cfqd = q->elevator->elevator_data;
struct cfq_queue *cfqq = RQ_CFQQ(rq);
cfq_remove_request(rq);
cfqq->on_dispatch[rq_is_sync(rq)]++;
elv_dispatch_sort(q, rq);
-
- rq = list_entry(q->queue_head.prev, struct request, queuelist);
- cfqd->last_sector = rq->sector + rq->nr_sectors;
}
/*
@@ -1585,6 +1581,7 @@
struct request *rq)
{
struct cfq_queue *cfqq = cfqd->active_queue;
+ sector_t dist;
if (cfq_class_idle(new_cfqq))
return 0;
@@ -1594,14 +1591,14 @@
if (cfq_class_idle(cfqq))
return 1;
- if (!cfq_cfqq_wait_request(new_cfqq))
- return 0;
+
/*
* if the new request is sync, but the currently running queue is
* not, let the sync request have priority.
*/
if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
return 1;
+
/*
* So both queues are sync. Let the new request get disk time if
* it's a metadata request and the current queue is doing regular IO.
@@ -1609,6 +1606,21 @@
if (rq_is_meta(rq) && !cfqq->meta_pending)
return 1;
+ if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
+ return 0;
+
+ /*
+ * if this request is as-good as one we would expect from the
+ * current cfqq, let it preempt
+ */
+ if (rq->sector > cfqd->last_sector)
+ dist = rq->sector - cfqd->last_sector;
+ else
+ dist = cfqd->last_sector - rq->sector;
+
+ if (dist <= cfqd->active_cic->seek_mean)
+ return 1;
+
return 0;
}
@@ -1719,6 +1731,8 @@
cfqq->on_dispatch[sync]--;
cfqq->service_last = now;
+ cfqd->last_sector = rq->hard_sector + rq->hard_nr_sectors;
+
if (!cfq_class_idle(cfqq))
cfqd->last_end_request = now;