cfq: async queue allocation per priority

If we have two processes with different ioprio_class, but the same
ioprio_data, their async requests will fall into the same queue. I guess
such behavior is not expected, because it's not right to put real-time
requests and best-effort requests in the same queue.

The attached patch fixes the problem by introducing additional *cfqq
fields on cfqd, pointing to per-(class,priority) async queues.

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

2 files changed, 52 insertions, 12 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9755a3cfad26..bc7190eed10d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -92,7 +92,11 @@ struct cfq_data {
         struct cfq_queue *active_queue;
         struct cfq_io_context *active_cic;
 
-        struct cfq_queue *async_cfqq[IOPRIO_BE_NR];
+        /*
+         * async queue for each priority case
+         */
+        struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
+        struct cfq_queue *async_idle_cfqq;
 
         struct timer_list idle_class_timer;
 
@@ -1414,24 +1418,44 @@ out:
         return cfqq;
 }
 
+static struct cfq_queue **
+cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
+{
+        switch(ioprio_class) {
+        case IOPRIO_CLASS_RT:
+                return &cfqd->async_cfqq[0][ioprio];
+        case IOPRIO_CLASS_BE:
+                return &cfqd->async_cfqq[1][ioprio];
+        case IOPRIO_CLASS_IDLE:
+                return &cfqd->async_idle_cfqq;
+        default:
+                BUG();
+        }
+}
+
 static struct cfq_queue *
 cfq_get_queue(struct cfq_data *cfqd, int is_sync, struct task_struct *tsk,
               gfp_t gfp_mask)
 {
         const int ioprio = task_ioprio(tsk);
+        const int ioprio_class = task_ioprio_class(tsk);
+        struct cfq_queue **async_cfqq = NULL;
         struct cfq_queue *cfqq = NULL;
 
-        if (!is_sync)
-                cfqq = cfqd->async_cfqq[ioprio];
+        if (!is_sync) {
+                async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
+                cfqq = *async_cfqq;
+        }
+
         if (!cfqq)
                 cfqq = cfq_find_alloc_queue(cfqd, is_sync, tsk, gfp_mask);
 
         /*
          * pin the queue now that it's allocated, scheduler exit will prune it
          */
-        if (!is_sync && !cfqd->async_cfqq[ioprio]) {
+        if (!is_sync && !(*async_cfqq)) {
                 atomic_inc(&cfqq->ref);
-                cfqd->async_cfqq[ioprio] = cfqq;
+                *async_cfqq = cfqq;
         }
 
         atomic_inc(&cfqq->ref);
@@ -2042,11 +2066,24 @@ static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
         blk_sync_queue(cfqd->queue);
 }
 
+static void cfq_put_async_queues(struct cfq_data *cfqd)
+{
+        int i;
+
+        for (i = 0; i < IOPRIO_BE_NR; i++) {
+                if (cfqd->async_cfqq[0][i])
+                        cfq_put_queue(cfqd->async_cfqq[0][i]);
+                if (cfqd->async_cfqq[1][i])
+                        cfq_put_queue(cfqd->async_cfqq[1][i]);
+                if (cfqd->async_idle_cfqq)
+                        cfq_put_queue(cfqd->async_idle_cfqq);
+        }
+}
+
 static void cfq_exit_queue(elevator_t *e)
 {
         struct cfq_data *cfqd = e->elevator_data;
         request_queue_t *q = cfqd->queue;
-        int i;
 
         cfq_shutdown_timer_wq(cfqd);
 
@@ -2063,12 +2100,7 @@ static void cfq_exit_queue(elevator_t *e)
                 __cfq_exit_single_io_context(cfqd, cic);
         }
 
-        /*
-         * Put the async queues
-         */
-        for (i = 0; i < IOPRIO_BE_NR; i++)
-                if (cfqd->async_cfqq[i])        
-                        cfq_put_queue(cfqd->async_cfqq[i]);
+        cfq_put_async_queues(cfqd);
 
         spin_unlock_irq(q->queue_lock);
 
diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
index 2eaa142cd061..baf29387cab4 100644
--- a/include/linux/ioprio.h
+++ b/include/linux/ioprio.h
@@ -53,6 +53,14 @@ static inline int task_ioprio(struct task_struct *task)
         return IOPRIO_NORM;
 }
 
+static inline int task_ioprio_class(struct task_struct *task)
+{
+        if (ioprio_valid(task->ioprio))
+                return IOPRIO_PRIO_CLASS(task->ioprio);
+
+        return IOPRIO_CLASS_BE;
+}
+
 static inline int task_nice_ioprio(struct task_struct *task)
 {
         return (task_nice(task) + 20) / 5;