block cfq: compensate preempted queue even if it has no slice assigned

If a queue is preempted before it gets slice assigned, the queue doesn't get
compensation, which looks unfair. For such queue, we compensate it for a whole
slice.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 7bfea53c1bb54c1c6b5fb3273b61760205a2dba2..501ffdf0399c9b848ac5379531b5aac8b0172a35 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -598,8 +598,8 @@ cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
        return cfq_target_latency * cfqg->weight / st->total_weight;
 }
 
-static inline void
-cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+static inline unsigned
+cfq_scaled_group_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 {
        unsigned slice = cfq_prio_to_slice(cfqd, cfqq);
        if (cfqd->cfq_latency) {
@@ -625,6 +625,14 @@ cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
                                    low_slice);
                }
        }
+       return slice;
+}
+
+static inline void
+cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+       unsigned slice = cfq_scaled_group_slice(cfqd, cfqq);
+
        cfqq->slice_start = jiffies;
        cfqq->slice_end = jiffies + slice;
        cfqq->allocated_slice = slice;
@@ -1661,8 +1669,11 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
        /*
         * store what was left of this slice, if the queue idled/timed out
         */
-       if (timed_out && !cfq_cfqq_slice_new(cfqq)) {
-               cfqq->slice_resid = cfqq->slice_end - jiffies;
+       if (timed_out) {
+               if (cfq_cfqq_slice_new(cfqq))
+                       cfqq->slice_resid = cfq_scaled_group_slice(cfqd, cfqq);
+               else
+                       cfqq->slice_resid = cfqq->slice_end - jiffies;
                cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
        }