cfq-iosched: defer slice activation to first request being active
This better matches what time the queue is actually spending doing
IO.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 7a8ef0f..d44402a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -171,6 +171,7 @@
CFQ_CFQQ_FLAG_idle_window, /* slice idling enabled */
CFQ_CFQQ_FLAG_prio_changed, /* task priority has changed */
CFQ_CFQQ_FLAG_queue_new, /* queue never been serviced */
+ CFQ_CFQQ_FLAG_slice_new, /* no requests dispatched in slice */
};
#define CFQ_CFQQ_FNS(name) \
@@ -196,6 +197,7 @@
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(queue_new);
+CFQ_CFQQ_FNS(slice_new);
#undef CFQ_CFQQ_FNS
static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsigned short);
@@ -231,6 +233,42 @@
}
/*
+ * Scale schedule slice based on io priority. Use the sync time slice only
+ * if a queue is marked sync and has sync io queued. A sync queue with async
+ * io only, should not get full sync slice length.
+ */
+static inline int
+cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+ const int base_slice = cfqd->cfq_slice[cfq_cfqq_sync(cfqq)];
+
+ WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
+
+ return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - cfqq->ioprio));
+}
+
+static inline void
+cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+ cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
+}
+
+/*
+ * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
+ * isn't valid until the first request from the dispatch is activated
+ * and the slice time set.
+ */
+static inline int cfq_slice_used(struct cfq_queue *cfqq)
+{
+ if (cfq_cfqq_slice_new(cfqq))
+ return 0;
+ if (time_before(jiffies, cfqq->slice_end))
+ return 0;
+
+ return 1;
+}
+
+/*
* Lifted from AS - choose which of rq1 and rq2 that is best served now.
* We choose the request that is closest to the head right now. Distance
* behind the head is penalized and only allowed to a certain extent.
@@ -632,6 +670,7 @@
cfqq->slice_left = 0;
cfq_clear_cfqq_must_alloc_slice(cfqq);
cfq_clear_cfqq_fifo_expire(cfqq);
+ cfq_mark_cfqq_slice_new(cfqq);
}
cfqd->active_queue = cfqq;
@@ -660,7 +699,7 @@
* store what was left of this slice, if the queue idled out
* or was preempted
*/
- if (time_after(cfqq->slice_end, now))
+ if (cfq_slice_used(cfqq))
cfqq->slice_left = cfqq->slice_end - now;
else
cfqq->slice_left = 0;
@@ -858,27 +897,6 @@
return NULL;
}
-/*
- * Scale schedule slice based on io priority. Use the sync time slice only
- * if a queue is marked sync and has sync io queued. A sync queue with async
- * io only, should not get full sync slice length.
- */
-static inline int
-cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
-{
- const int base_slice = cfqd->cfq_slice[cfq_cfqq_sync(cfqq)];
-
- WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
-
- return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - cfqq->ioprio));
-}
-
-static inline void
-cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
-{
- cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
-}
-
static inline int
cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
@@ -894,7 +912,6 @@
*/
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
{
- unsigned long now = jiffies;
struct cfq_queue *cfqq;
cfqq = cfqd->active_queue;
@@ -904,7 +921,7 @@
/*
* slice has expired
*/
- if (!cfq_cfqq_must_dispatch(cfqq) && time_after(now, cfqq->slice_end))
+ if (!cfq_cfqq_must_dispatch(cfqq) && cfq_slice_used(cfqq))
goto expire;
/*
@@ -913,7 +930,7 @@
*/
if (!RB_EMPTY_ROOT(&cfqq->sort_list))
goto keep_queue;
- else if (cfq_cfqq_dispatched(cfqq)) {
+ else if (cfq_cfqq_slice_new(cfqq) || cfq_cfqq_dispatched(cfqq)) {
cfqq = NULL;
goto keep_queue;
} else if (cfq_cfqq_class_sync(cfqq)) {
@@ -965,20 +982,15 @@
} while (dispatched < max_dispatch);
/*
- * if slice end isn't set yet, set it.
- */
- if (!cfqq->slice_end)
- cfq_set_prio_slice(cfqd, cfqq);
-
- /*
* expire an async queue immediately if it has used up its slice. idle
* queue always expire after 1 dispatch round.
*/
if ((!cfq_cfqq_sync(cfqq) &&
cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
- cfq_class_idle(cfqq) ||
- !cfq_cfqq_idle_window(cfqq))
+ cfq_class_idle(cfqq)) {
+ cfqq->slice_end = jiffies + 1;
cfq_slice_expired(cfqd, 0);
+ }
return dispatched;
}
@@ -1612,7 +1624,8 @@
BUG_ON(!cfq_cfqq_on_rr(cfqq));
list_move(&cfqq->cfq_list, &cfqd->cur_rr);
- cfqq->slice_end = cfqq->slice_left + jiffies;
+ cfqq->slice_end = 0;
+ cfq_mark_cfqq_slice_new(cfqq);
}
/*
@@ -1722,7 +1735,11 @@
* or if we want to idle in case it has no pending requests.
*/
if (cfqd->active_queue == cfqq) {
- if (time_after(now, cfqq->slice_end))
+ if (cfq_cfqq_slice_new(cfqq)) {
+ cfq_set_prio_slice(cfqd, cfqq);
+ cfq_clear_cfqq_slice_new(cfqq);
+ }
+ if (cfq_slice_used(cfqq))
cfq_slice_expired(cfqd, 0);
else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list)) {
if (!cfq_arm_slice_timer(cfqd, cfqq))
@@ -1901,12 +1918,10 @@
spin_lock_irqsave(cfqd->queue->queue_lock, flags);
if ((cfqq = cfqd->active_queue) != NULL) {
- unsigned long now = jiffies;
-
/*
* expired
*/
- if (time_after(now, cfqq->slice_end))
+ if (cfq_slice_used(cfqq))
goto expire;
/*