[PATCH 2/2]block cfq: compensate preempted queue even if it has no slice assigned

[Shaohua Li <shaohua.li@intel.com>]

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>

---
 block/cfq-iosched.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

Index: linux/block/cfq-iosched.c
===================================================================
--- linux.orig/block/cfq-iosched.c	2011-01-10 15:37:33.000000000 +0800
+++ linux/block/cfq-iosched.c	2011-01-10 15:54:28.000000000 +0800
@@ -605,8 +605,8 @@ cfq_group_slice(struct cfq_data *cfqd, s
 	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) {
@@ -632,6 +632,14 @@ cfq_set_prio_slice(struct cfq_data *cfqd
 				    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;
@@ -1672,8 +1680,11 @@ __cfq_slice_expired(struct cfq_data *cfq
 	/*
 	 * 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);
 	}