cfq-iosched: make io priorities inherit CPU scheduling class as well as nice

We currently set all processes to the best-effort scheduling class,
regardless of what CPU scheduling class they belong to. Improve that
so that we correctly track idle and rt scheduling classes as well.

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

2 files changed, 16 insertions, 2 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 7f909d2f4886..b399c62936e0 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1303,10 +1303,10 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
                 printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
         case IOPRIO_CLASS_NONE:
                 /*
-                 * no prio set, place us in the middle of the BE classes
+                 * no prio set, inherit CPU scheduling settings
                  */
                 cfqq->ioprio = task_nice_ioprio(tsk);
-                cfqq->ioprio_class = IOPRIO_CLASS_BE;
+                cfqq->ioprio_class = task_nice_ioclass(tsk);
                 break;
         case IOPRIO_CLASS_RT:
                 cfqq->ioprio = task_ioprio(ioc);
diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
index 2a3bb1bb7433..f98a656b17e5 100644
--- a/include/linux/ioprio.h
+++ b/include/linux/ioprio.h
@@ -68,6 +68,20 @@ static inline int task_nice_ioprio(struct task_struct *task)
 }
 
 /*
+ * This is for the case where the task hasn't asked for a specific IO class.
+ * Check for idle and rt task process, and return appropriate IO class.
+ */
+static inline int task_nice_ioclass(struct task_struct *task)
+{
+        if (task->policy == SCHED_IDLE)
+                return IOPRIO_CLASS_IDLE;
+        else if (task->policy == SCHED_FIFO || task->policy == SCHED_RR)
+                return IOPRIO_CLASS_RT;
+        else
+                return IOPRIO_CLASS_BE;
+}
+
+/*
  * For inheritance, return the highest of the two given priorities
  */
 extern int ioprio_best(unsigned short aprio, unsigned short bprio);