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>

1 files changed, 67 insertions, 54 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 690ebd96dc42..5c3cee93329a 100644
--- 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);