cfq-iosched: abstract out the 'may this cfqq dispatch' logic

Makes the whole thing easier to read, cfq_dispatch_requests() was
a bit messy before.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 690ebd9..5c3cee9 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1247,67 +1247,21 @@ static int cfq_forced_dispatch(struct cfq_data *cfqd)
        return dispatched;
 }
 
-/*
- * Dispatch a request from cfqq, moving them to the request queue
- * dispatch list.
- */
-static void cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 {
-       struct request *rq;
-
-       BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
-
-       /*
-        * follow expired path, else get first next available
-        */
-       rq = cfq_check_fifo(cfqq);
-       if (!rq)
-               rq = cfqq->next_rq;
-
-       /*
-        * insert request into driver dispatch list
-        */
-       cfq_dispatch_insert(cfqd->queue, rq);
-
-       if (!cfqd->active_cic) {
-               struct cfq_io_context *cic = RQ_CIC(rq);
-
-               atomic_long_inc(&cic->ioc->refcount);
-               cfqd->active_cic = cic;
-       }
-}
-
-/*
- * Find the cfqq that we need to service and move a request from that to the
- * dispatch list
- */
-static int cfq_dispatch_requests(struct request_queue *q, int force)
-{
-       struct cfq_data *cfqd = q->elevator->elevator_data;
-       struct cfq_queue *cfqq;
        unsigned int max_dispatch;
 
-       if (!cfqd->busy_queues)
-               return 0;
-
-       if (unlikely(force))
-               return cfq_forced_dispatch(cfqd);
-
-       cfqq = cfq_select_queue(cfqd);
-       if (!cfqq)
-               return 0;
-
        /*
         * Drain async requests before we start sync IO
         */
        if (cfq_cfqq_idle_window(cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC])
-               return 0;
+               return false;
 
        /*
         * If this is an async queue and we have sync IO in flight, let it wait
         */
        if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
-               return 0;
+               return false;
 
        max_dispatch = cfqd->cfq_quantum;
        if (cfq_class_idle(cfqq))
@@ -1321,13 +1275,13 @@ static int cfq_dispatch_requests(struct request_queue *q, int force)
                 * idle queue must always only have a single IO in flight
                 */
                if (cfq_class_idle(cfqq))
-                       return 0;
+                       return false;
 
                /*
                 * We have other queues, don't allow more IO from this one
                 */
                if (cfqd->busy_queues > 1)
-                       return 0;
+                       return false;
 
                /*
                 * Sole queue user, allow bigger slice
@@ -1351,13 +1305,72 @@ static int cfq_dispatch_requests(struct request_queue *q, int force)
                        max_dispatch = depth;
        }
 
-       if (cfqq->dispatched >= max_dispatch)
+       /*
+        * If we're below the current max, allow a dispatch
+        */
+       return cfqq->dispatched < max_dispatch;
+}
+
+/*
+ * Dispatch a request from cfqq, moving them to the request queue
+ * dispatch list.
+ */
+static bool cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+       struct request *rq;
+
+       BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
+
+       if (!cfq_may_dispatch(cfqd, cfqq))
+               return false;
+
+       /*
+        * follow expired path, else get first next available
+        */
+       rq = cfq_check_fifo(cfqq);
+       if (!rq)
+               rq = cfqq->next_rq;
+
+       /*
+        * insert request into driver dispatch list
+        */
+       cfq_dispatch_insert(cfqd->queue, rq);
+
+       if (!cfqd->active_cic) {
+               struct cfq_io_context *cic = RQ_CIC(rq);
+
+               atomic_long_inc(&cic->ioc->refcount);
+               cfqd->active_cic = cic;
+       }
+
+       return true;
+}
+
+/*
+ * Find the cfqq that we need to service and move a request from that to the
+ * dispatch list
+ */
+static int cfq_dispatch_requests(struct request_queue *q, int force)
+{
+       struct cfq_data *cfqd = q->elevator->elevator_data;
+       struct cfq_queue *cfqq;
+
+       if (!cfqd->busy_queues)
+               return 0;
+
+       if (unlikely(force))
+               return cfq_forced_dispatch(cfqd);
+
+       cfqq = cfq_select_queue(cfqd);
+       if (!cfqq)
                return 0;
 
        /*
-        * Dispatch a request from this cfqq
+        * Dispatch a request from this cfqq, if it is allowed
         */
-       cfq_dispatch_request(cfqd, cfqq);
+       if (!cfq_dispatch_request(cfqd, cfqq))
+               return 0;
+
        cfqq->slice_dispatch++;
        cfq_clear_cfqq_must_dispatch(cfqq);