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>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 7f909d2f4886d36aaea83836a07a9d255d3e7de5..b399c62936e01a503715273ffef29ac2fafef8a4 100644 (file)
--- 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 2a3bb1bb74336f27c27f6627153900d46d6c178a..f98a656b17e5b4b732e57e0e70e4eb5ec53bce84 100644 (file)
--- a/include/linux/ioprio.h
+++ b/include/linux/ioprio.h
@@ -67,6 +67,20 @@ static inline int task_nice_ioprio(struct task_struct *task)
        return (task_nice(task) + 20) / 5;
 }
 
+/*
+ * 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
  */