1 files changed, 15 insertions, 9 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c2ef5d17608c..47abd24617be 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -191,8 +191,14 @@ struct cfq_data {
          */
         int rq_queued;
         int hw_tag;
-        int hw_tag_samples;
-        int rq_in_driver_peak;
+        /*
+         * hw_tag can be
+         * -1 => indeterminate, (cfq will behave as if NCQ is present, to allow better detection)
+         *  1 => NCQ is present (hw_tag_est_depth is the estimated max depth)
+         *  0 => no NCQ
+         */
+        int hw_tag_est_depth;
+        unsigned int hw_tag_samples;
 
         /*
          * idle window management
@@ -2518,8 +2524,11 @@ 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);
+        if (rq_in_driver(cfqd) > cfqd->hw_tag_est_depth)
+                cfqd->hw_tag_est_depth = rq_in_driver(cfqd);
+
+        if (cfqd->hw_tag == 1)
+                return;
 
         if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
             rq_in_driver(cfqd) <= CFQ_HW_QUEUE_MIN)
@@ -2538,13 +2547,10 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
         if (cfqd->hw_tag_samples++ < 50)
                 return;
 
-        if (cfqd->rq_in_driver_peak >= CFQ_HW_QUEUE_MIN)
+        if (cfqd->hw_tag_est_depth >= CFQ_HW_QUEUE_MIN)
                 cfqd->hw_tag = 1;
         else
                 cfqd->hw_tag = 0;
-
-        cfqd->hw_tag_samples = 0;
-        cfqd->rq_in_driver_peak = 0;
 }
 
 static void cfq_completed_request(struct request_queue *q, struct request *rq)
@@ -2951,7 +2957,7 @@ static void *cfq_init_queue(struct request_queue *q)
         cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
         cfqd->cfq_slice_idle = cfq_slice_idle;
         cfqd->cfq_latency = 1;
-        cfqd->hw_tag = 1;
+        cfqd->hw_tag = -1;
         cfqd->last_end_sync_rq = jiffies;
         return cfqd;
 }