blkio: Wait for cfq queue to get backlogged if group is empty

[safe/jmp/linux-2.6] / block / cfq-iosched.c

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f736462..1cc1048 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -117,6 +117,7 @@ struct cfq_queue {
 
        /* time when queue got scheduled in to dispatch first request. */
        unsigned long dispatch_start;
+       unsigned int allocated_slice;
        /* time when first request from queue completed and slice started. */
        unsigned long slice_start;
        unsigned long slice_end;
@@ -314,6 +315,8 @@ enum cfqq_state_flags {
        CFQ_CFQQ_FLAG_sync,             /* synchronous queue */
        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)                                             \
@@ -341,6 +344,8 @@ CFQ_CFQQ_FNS(slice_new);
 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
@@ -578,6 +583,7 @@ cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
        }
        cfqq->slice_start = jiffies;
        cfqq->slice_end = jiffies + slice;
+       cfqq->allocated_slice = slice;
        cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
 }
 
@@ -859,7 +865,7 @@ cfq_group_service_tree_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
 
 static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq)
 {
-       unsigned int slice_used, allocated_slice;
+       unsigned int slice_used;
 
        /*
         * Queue got expired before even a single request completed or
@@ -876,9 +882,8 @@ static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq)
                                        1);
        } else {
                slice_used = jiffies - cfqq->slice_start;
-               allocated_slice = cfqq->slice_end - cfqq->slice_start;
-               if (slice_used > allocated_slice)
-                       slice_used = allocated_slice;
+               if (slice_used > cfqq->allocated_slice)
+                       slice_used = cfqq->allocated_slice;
        }
 
        cfq_log_cfqq(cfqq->cfqd, cfqq, "sl_used=%u sect=%lu", slice_used,
@@ -1495,6 +1500,7 @@ static void __cfq_set_active_queue(struct cfq_data *cfqd,
                cfq_log_cfqq(cfqd, cfqq, "set_active");
                cfqq->slice_start = 0;
                cfqq->dispatch_start = jiffies;
+               cfqq->allocated_slice = 0;
                cfqq->slice_end = 0;
                cfqq->slice_dispatch = 0;
                cfqq->nr_sectors = 0;
@@ -1524,6 +1530,8 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                del_timer(&cfqd->idle_slice_timer);
 
        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
@@ -2066,7 +2074,8 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
        /*
         * The active queue has run out of time, expire it and select new.
         */
-       if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq))
+       if ((cfq_slice_used(cfqq) || cfq_cfqq_wait_busy_done(cfqq))
+            && !cfq_cfqq_must_dispatch(cfqq))
                goto expire;
 
        /*
@@ -3096,6 +3105,10 @@ 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
@@ -3214,6 +3227,17 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
                        cfq_set_prio_slice(cfqd, cfqq);
                        cfq_clear_cfqq_slice_new(cfqq);
                }
+
+               /*
+                * If this queue consumed its slice and this is last queue
+                * in the group, wait for next request before we expire
+                * the queue
+                */
+               if (cfq_slice_used(cfqq) && cfqq->cfqg->nr_cfqq == 1) {
+                       cfqq->slice_end = jiffies + cfqd->cfq_slice_idle;
+                       cfq_mark_cfqq_wait_busy(cfqq);
+               }
+
                /*
                 * Idling is not enabled on:
                 * - expired queues