1 files changed, 75 insertions, 19 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index cfb0b2f5f63d..e2f80463ed0d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -283,7 +283,7 @@ struct cfq_data {
          */
         struct cfq_queue oom_cfqq;
 
-        unsigned long last_end_sync_rq;
+        unsigned long last_delayed_sync;
 
         /* List of cfq groups being managed on this device*/
         struct hlist_head cfqg_list;
@@ -319,7 +319,6 @@ enum cfqq_state_flags {
         CFQ_CFQQ_FLAG_coop,             /* cfqq is shared */
         CFQ_CFQQ_FLAG_deep,             /* sync cfqq experienced large depth */
         CFQ_CFQQ_FLAG_wait_busy,        /* Waiting for next request */
-        CFQ_CFQQ_FLAG_wait_busy_done,   /* Got new request. Expire the queue */
 };
 
 #define CFQ_CFQQ_FNS(name)                                              \
@@ -348,7 +347,6 @@ CFQ_CFQQ_FNS(sync);
 CFQ_CFQQ_FNS(coop);
 CFQ_CFQQ_FNS(deep);
 CFQ_CFQQ_FNS(wait_busy);
-CFQ_CFQQ_FNS(wait_busy_done);
 #undef CFQ_CFQQ_FNS
 
 #ifdef CONFIG_DEBUG_CFQ_IOSCHED
@@ -1574,7 +1572,6 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 
         cfq_clear_cfqq_wait_request(cfqq);
         cfq_clear_cfqq_wait_busy(cfqq);
-        cfq_clear_cfqq_wait_busy_done(cfqq);
 
         /*
          * store what was left of this slice, if the queue idled/timed out
@@ -1750,6 +1747,12 @@ static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
                 return NULL;
 
         /*
+         * Don't search priority tree if it's the only queue in the group.
+         */
+        if (cur_cfqq->cfqg->nr_cfqq == 1)
+                return NULL;
+
+        /*
          * We should notice if some of the queues are cooperating, eg
          * working closely on the same area of the disk. In that case,
          * we can group them together and don't waste time idling.
@@ -2110,7 +2113,9 @@ static void cfq_choose_cfqg(struct cfq_data *cfqd)
                 cfqd->workload_expires = jiffies + cfqg->saved_workload_slice;
                 cfqd->serving_type = cfqg->saved_workload;
                 cfqd->serving_prio = cfqg->saved_serving_prio;
-        }
+        } else
+                cfqd->workload_expires = jiffies - 1;
+
         choose_service_tree(cfqd, cfqg);
 }
 
@@ -2128,14 +2133,35 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
 
         if (!cfqd->rq_queued)
                 return NULL;
+
         /*
-         * The active queue has run out of time, expire it and select new.
+         * We were waiting for group to get backlogged. Expire the queue
          */
-        if ((cfq_slice_used(cfqq) || cfq_cfqq_wait_busy_done(cfqq))
-             && !cfq_cfqq_must_dispatch(cfqq))
+        if (cfq_cfqq_wait_busy(cfqq) && !RB_EMPTY_ROOT(&cfqq->sort_list))
                 goto expire;
 
         /*
+         * The active queue has run out of time, expire it and select new.
+         */
+        if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) {
+                /*
+                 * If slice had not expired at the completion of last request
+                 * we might not have turned on wait_busy flag. Don't expire
+                 * the queue yet. Allow the group to get backlogged.
+                 *
+                 * The very fact that we have used the slice, that means we
+                 * have been idling all along on this queue and it should be
+                 * ok to wait for this request to complete.
+                 */
+                if (cfqq->cfqg->nr_cfqq == 1 && RB_EMPTY_ROOT(&cfqq->sort_list)
+                    && cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
+                        cfqq = NULL;
+                        goto keep_queue;
+                } else
+                        goto expire;
+        }
+
+        /*
          * The active queue has requests and isn't expired, allow it to
          * dispatch.
          */
@@ -2264,7 +2290,7 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
          * based on the last sync IO we serviced
          */
         if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
-                unsigned long last_sync = jiffies - cfqd->last_end_sync_rq;
+                unsigned long last_sync = jiffies - cfqd->last_delayed_sync;
                 unsigned int depth;
 
                 depth = last_sync / cfqd->cfq_slice[1];
@@ -3165,10 +3191,6 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         cfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
 
         if (cfqq == cfqd->active_queue) {
-                if (cfq_cfqq_wait_busy(cfqq)) {
-                        cfq_clear_cfqq_wait_busy(cfqq);
-                        cfq_mark_cfqq_wait_busy_done(cfqq);
-                }
                 /*
                  * Remember that we saw a request from this process, but
                  * don't start queuing just yet. Otherwise we risk seeing lots
@@ -3183,6 +3205,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                         if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE ||
                             cfqd->busy_queues > 1) {
                                 del_timer(&cfqd->idle_slice_timer);
+                                cfq_clear_cfqq_wait_request(cfqq);
                                 __blk_run_queue(cfqd->queue);
                         } else
                                 cfq_mark_cfqq_must_dispatch(cfqq);
@@ -3251,6 +3274,35 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
                 cfqd->hw_tag = 0;
 }
 
+static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+        struct cfq_io_context *cic = cfqd->active_cic;
+
+        /* If there are other queues in the group, don't wait */
+        if (cfqq->cfqg->nr_cfqq > 1)
+                return false;
+
+        if (cfq_slice_used(cfqq))
+                return true;
+
+        /* if slice left is less than think time, wait busy */
+        if (cic && sample_valid(cic->ttime_samples)
+            && (cfqq->slice_end - jiffies < cic->ttime_mean))
+                return true;
+
+        /*
+         * If think times is less than a jiffy than ttime_mean=0 and above
+         * will not be true. It might happen that slice has not expired yet
+         * but will expire soon (4-5 ns) during select_queue(). To cover the
+         * case where think time is less than a jiffy, mark the queue wait
+         * busy if only 1 jiffy is left in the slice.
+         */
+        if (cfqq->slice_end - jiffies == 1)
+                return true;
+
+        return false;
+}
+
 static void cfq_completed_request(struct request_queue *q, struct request *rq)
 {
         struct cfq_queue *cfqq = RQ_CFQQ(rq);
@@ -3273,7 +3325,8 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
 
         if (sync) {
                 RQ_CIC(rq)->last_end_request = now;
-                cfqd->last_end_sync_rq = now;
+                if (!time_after(rq->start_time + cfqd->cfq_fifo_expire[1], now))
+                        cfqd->last_delayed_sync = now;
         }
 
         /*
@@ -3289,11 +3342,10 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
                 }
 
                 /*
-                 * If this queue consumed its slice and this is last queue
-                 * in the group, wait for next request before we expire
-                 * the queue
+                 * Should we wait for next request to come in before we expire
+                 * the queue.
                  */
-                if (cfq_slice_used(cfqq) && cfqq->cfqg->nr_cfqq == 1) {
+                if (cfq_should_wait_busy(cfqd, cfqq)) {
                         cfqq->slice_end = jiffies + cfqd->cfq_slice_idle;
                         cfq_mark_cfqq_wait_busy(cfqq);
                 }
@@ -3711,7 +3763,11 @@ static void *cfq_init_queue(struct request_queue *q)
         cfqd->cfq_latency = 1;
         cfqd->cfq_group_isolation = 0;
         cfqd->hw_tag = -1;
-        cfqd->last_end_sync_rq = jiffies;
+        /*
+         * we optimistically start assuming sync ops weren't delayed in last
+         * second, in order to have larger depth for async operations.
+         */
+        cfqd->last_delayed_sync = jiffies - HZ;
         INIT_RCU_HEAD(&cfqd->rcu);
         return cfqd;
 }