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>

1 files changed, 12 insertions, 0 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 47d6aaca0c51..418da9a49bb0 100644
--- 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;