cfq-iosched: improve hw_tag detection

If active queue hasn't enough requests and idle window opens, cfq will not
dispatch sufficient requests to hardware. In such situation, current code
will zero hw_tag. But this is because cfq doesn't dispatch enough requests
instead of hardware queue doesn't work. Don't zero hw_tag in such case.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 47d6aaca0c51809f7d4098b2b557d080a4fc45c8..418da9a49bb011a241098e65f4ff90343854788b 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2257,6 +2257,8 @@ static void cfq_insert_request(struct request_queue *q, struct request *rq)
  */
 static void cfq_update_hw_tag(struct cfq_data *cfqd)
 {
+       struct cfq_queue *cfqq = cfqd->active_queue;
+
        if (rq_in_driver(cfqd) > cfqd->rq_in_driver_peak)
                cfqd->rq_in_driver_peak = rq_in_driver(cfqd);
 
@@ -2264,6 +2266,16 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
            rq_in_driver(cfqd) <= CFQ_HW_QUEUE_MIN)
                return;
 
+       /*
+        * If active queue hasn't enough requests and can idle, cfq might not
+        * dispatch sufficient requests to hardware. Don't zero hw_tag in this
+        * case
+        */
+       if (cfqq && cfq_cfqq_idle_window(cfqq) &&
+           cfqq->dispatched + cfqq->queued[0] + cfqq->queued[1] <
+           CFQ_HW_QUEUE_MIN && rq_in_driver(cfqd) < CFQ_HW_QUEUE_MIN)
+               return;
+
        if (cfqd->hw_tag_samples++ < 50)
                return;