block: improve queue_should_plug() by looking at IO depths
Instead of just checking whether this device uses block layer
tagging, we can improve the detection by looking at the maximum
queue depth it has reached. If that crosses 4, then deem it a
queuing device.
This is important on high IOPS devices, since plugging hurts
the performance there (it can be as much as 10-15% of the sys
time).
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-core.c b/block/blk-core.c
index 5255971..93051d1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1146,7 +1146,7 @@
*/
static inline bool queue_should_plug(struct request_queue *q)
{
- return !(blk_queue_nonrot(q) && blk_queue_tagged(q));
+ return !(blk_queue_nonrot(q) && blk_queue_queuing(q));
}
static int __make_request(struct request_queue *q, struct bio *bio)
@@ -1857,8 +1857,15 @@
* and to it is freed is accounted as io that is in progress at
* the driver side.
*/
- if (blk_account_rq(rq))
+ if (blk_account_rq(rq)) {
q->in_flight[rq_is_sync(rq)]++;
+ /*
+ * Mark this device as supporting hardware queuing, if
+ * we have more IOs in flight than 4.
+ */
+ if (!blk_queue_queuing(q) && queue_in_flight(q) > 4)
+ set_bit(QUEUE_FLAG_CQ, &q->queue_flags);
+ }
}
/**