cfq-iosched: delay async IO dispatch, if sync IO was just done
o Do not allow more than max_dispatch requests from an async queue, if some
sync request has finished recently. This is in the hope that sync activity
is still going on in the system and we might receive a sync request soon.
Most likely from a sync queue which finished a request and we did not enable
idling on it.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 8917f2b..70b48ea 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -181,6 +181,8 @@
* Fallback dummy cfqq for extreme OOM conditions
*/
struct cfq_queue oom_cfqq;
+
+ unsigned long last_end_sync_rq;
};
enum cfqq_state_flags {
@@ -1314,6 +1316,8 @@
* Does this cfqq already have too much IO in flight?
*/
if (cfqq->dispatched >= max_dispatch) {
+ unsigned long load_at = cfqd->last_end_sync_rq + cfq_slice_sync;
+
/*
* idle queue must always only have a single IO in flight
*/
@@ -1327,6 +1331,14 @@
return 0;
/*
+ * If a sync request has completed recently, don't overload
+ * the dispatch queue yet with async requests.
+ */
+ if (cfqd->cfq_desktop && !cfq_cfqq_sync(cfqq)
+ && time_before(jiffies, load_at))
+ return 0;
+
+ /*
* we are the only queue, allow up to 4 times of 'quantum'
*/
if (cfqq->dispatched >= 4 * max_dispatch)
@@ -2158,8 +2170,10 @@
if (cfq_cfqq_sync(cfqq))
cfqd->sync_flight--;
- if (sync)
+ if (sync) {
RQ_CIC(rq)->last_end_request = now;
+ cfqd->last_end_sync_rq = now;
+ }
/*
* If this is the active queue, check if it needs to be expired,
@@ -2483,7 +2497,7 @@
cfqd->cfq_slice_idle = cfq_slice_idle;
cfqd->cfq_desktop = 1;
cfqd->hw_tag = 1;
-
+ cfqd->last_end_sync_rq = jiffies;
return cfqd;
}