[PATCH] block: Improve think time sampling for CFQ

[Divyesh Shah <dpshah@google.com>]

Avoid taking a think time sample when the cfqq is not a sync queue or not
currently active or till its first request in the ongoing timeslice
completes.

Signed-off by: Divyesh Shah <dpshah@google.com>
---
This applies to Linus's kernel tree.

 block/cfq-iosched.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index fd7080e..1657d4f 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1904,10 +1904,17 @@ err:
 }
 
 static void
-cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
+cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
+			struct cfq_io_context *cic)
 {
-	unsigned long elapsed = jiffies - cic->last_end_request;
-	unsigned long ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);
+	unsigned long elapsed, ttime;
+
+	if (!cfq_cfqq_sync(cfqq) || cfqq != cfqd->active_queue || 
+	    cfq_cfqq_slice_new(cfqq))
+		return;
+
+	elapsed = jiffies - cic->last_end_request;
+	ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);
 
 	cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
 	cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
@@ -2072,7 +2079,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 	if (rq_is_meta(rq))
 		cfqq->meta_pending++;
 
-	cfq_update_io_thinktime(cfqd, cic);
+	cfq_update_io_thinktime(cfqd, cfqq, cic);
 	cfq_update_io_seektime(cfqd, cic, rq);
 	cfq_update_idle_window(cfqd, cfqq, cic);