[PATCH] cfq-iosched: many performance fixes
This is a collection of patches that greatly improve CFQ performance
in some circumstances.
- Change the idling logic to only kick in after a request is done and we
are deciding what to do. Before the idling included the request service
time, so it was hard to adjust. Now it's true think/idle time.
- Take advantage of TCQ/NCQ/queueing for seeky sync workloads, but keep
it in control for sync and sequential (or close to) workloads.
- Expire queues immediately and move on to other busy queues, if we are
not going to idle after the current one finishes.
- Don't rearm idle timer if there are no busy queues. Just leave the
system idle.
Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 84b75f8..13c4793 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -26,7 +26,7 @@
static const int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static const int cfq_slice_async_rq = 2;
-static int cfq_slice_idle = HZ / 70;
+static int cfq_slice_idle = HZ / 125;
#define CFQ_IDLE_GRACE (HZ / 10)
#define CFQ_SLICE_SCALE (5)
@@ -906,6 +906,8 @@
return cfqq;
}
+#define CIC_SEEKY(cic) ((cic)->seek_mean > (128 * 1024))
+
static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
@@ -939,7 +941,7 @@
* fair distribution of slice time for a process doing back-to-back
* seeks. so allow a little bit of time for him to submit a new rq
*/
- if (sample_valid(cic->seek_samples) && cic->seek_mean > 131072)
+ if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
sl = 2;
mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
@@ -1038,8 +1040,10 @@
*/
if (!RB_EMPTY(&cfqq->sort_list))
goto keep_queue;
- else if (cfq_cfqq_class_sync(cfqq) &&
- time_before(now, cfqq->slice_end)) {
+ else if (cfq_cfqq_dispatched(cfqq)) {
+ cfqq = NULL;
+ goto keep_queue;
+ } else if (cfq_cfqq_class_sync(cfqq)) {
if (cfq_arm_slice_timer(cfqd, cfqq))
return NULL;
}
@@ -1088,8 +1092,7 @@
} while (dispatched < max_dispatch);
/*
- * if slice end isn't set yet, set it. if at least one request was
- * sync, use the sync time slice value
+ * if slice end isn't set yet, set it.
*/
if (!cfqq->slice_end)
cfq_set_prio_slice(cfqd, cfqq);
@@ -1100,7 +1103,8 @@
*/
if ((!cfq_cfqq_sync(cfqq) &&
cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
- cfq_class_idle(cfqq))
+ cfq_class_idle(cfqq) ||
+ !cfq_cfqq_idle_window(cfqq))
cfq_slice_expired(cfqd, 0);
return dispatched;
@@ -1109,10 +1113,11 @@
static int
cfq_forced_dispatch_cfqqs(struct list_head *list)
{
- int dispatched = 0;
struct cfq_queue *cfqq, *next;
struct cfq_rq *crq;
+ int dispatched;
+ dispatched = 0;
list_for_each_entry_safe(cfqq, next, list, cfq_list) {
while ((crq = cfqq->next_crq)) {
cfq_dispatch_insert(cfqq->cfqd->queue, crq);
@@ -1120,6 +1125,7 @@
}
BUG_ON(!list_empty(&cfqq->fifo));
}
+
return dispatched;
}
@@ -1146,7 +1152,8 @@
cfq_dispatch_requests(request_queue_t *q, int force)
{
struct cfq_data *cfqd = q->elevator->elevator_data;
- struct cfq_queue *cfqq;
+ struct cfq_queue *cfqq, *prev_cfqq;
+ int dispatched;
if (!cfqd->busy_queues)
return 0;
@@ -1154,10 +1161,17 @@
if (unlikely(force))
return cfq_forced_dispatch(cfqd);
- cfqq = cfq_select_queue(cfqd);
- if (cfqq) {
+ dispatched = 0;
+ prev_cfqq = NULL;
+ while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
int max_dispatch;
+ /*
+ * Don't repeat dispatch from the previous queue.
+ */
+ if (prev_cfqq == cfqq)
+ break;
+
cfq_clear_cfqq_must_dispatch(cfqq);
cfq_clear_cfqq_wait_request(cfqq);
del_timer(&cfqd->idle_slice_timer);
@@ -1166,10 +1180,19 @@
if (cfq_class_idle(cfqq))
max_dispatch = 1;
- return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
+ dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
+
+ /*
+ * If the dispatch cfqq has idling enabled and is still
+ * the active queue, break out.
+ */
+ if (cfq_cfqq_idle_window(cfqq) && cfqd->active_queue)
+ break;
+
+ prev_cfqq = cfqq;
}
- return 0;
+ return dispatched;
}
/*
@@ -1375,24 +1398,28 @@
{
struct cfq_data *cfqd = cic->key;
struct cfq_queue *cfqq;
- if (cfqd) {
- spin_lock(cfqd->queue->queue_lock);
- cfqq = cic->cfqq[ASYNC];
- if (cfqq) {
- struct cfq_queue *new_cfqq;
- new_cfqq = cfq_get_queue(cfqd, CFQ_KEY_ASYNC,
- cic->ioc->task, GFP_ATOMIC);
- if (new_cfqq) {
- cic->cfqq[ASYNC] = new_cfqq;
- cfq_put_queue(cfqq);
- }
- }
- cfqq = cic->cfqq[SYNC];
- if (cfqq)
- cfq_mark_cfqq_prio_changed(cfqq);
- spin_unlock(cfqd->queue->queue_lock);
+ if (unlikely(!cfqd))
+ return;
+
+ spin_lock(cfqd->queue->queue_lock);
+
+ cfqq = cic->cfqq[ASYNC];
+ if (cfqq) {
+ struct cfq_queue *new_cfqq;
+ new_cfqq = cfq_get_queue(cfqd, CFQ_KEY_ASYNC, cic->ioc->task,
+ GFP_ATOMIC);
+ if (new_cfqq) {
+ cic->cfqq[ASYNC] = new_cfqq;
+ cfq_put_queue(cfqq);
+ }
}
+
+ cfqq = cic->cfqq[SYNC];
+ if (cfqq)
+ cfq_mark_cfqq_prio_changed(cfqq);
+
+ spin_unlock(cfqd->queue->queue_lock);
}
/*
@@ -1461,8 +1488,7 @@
* set ->slice_left to allow preemption for a new process
*/
cfqq->slice_left = 2 * cfqd->cfq_slice_idle;
- if (!cfqd->hw_tag)
- cfq_mark_cfqq_idle_window(cfqq);
+ cfq_mark_cfqq_idle_window(cfqq);
cfq_mark_cfqq_prio_changed(cfqq);
cfq_init_prio_data(cfqq);
}
@@ -1653,7 +1679,8 @@
{
int enable_idle = cfq_cfqq_idle_window(cfqq);
- if (!cic->ioc->task || !cfqd->cfq_slice_idle || cfqd->hw_tag)
+ if (!cic->ioc->task || !cfqd->cfq_slice_idle ||
+ (cfqd->hw_tag && CIC_SEEKY(cic)))
enable_idle = 0;
else if (sample_valid(cic->ttime_samples)) {
if (cic->ttime_mean > cfqd->cfq_slice_idle)
@@ -1683,7 +1710,7 @@
return 0;
if (!cfqq)
- return 1;
+ return 0;
if (cfq_class_idle(cfqq))
return 1;
@@ -1715,7 +1742,7 @@
cfqq->slice_left = cfq_prio_to_slice(cfqd, cfqq) / 2;
cfqq->slice_end = cfqq->slice_left + jiffies;
- __cfq_slice_expired(cfqd, cfqq, 1);
+ cfq_slice_expired(cfqd, 1);
__cfq_set_active_queue(cfqd, cfqq);
}
@@ -1834,11 +1861,23 @@
cfqq->service_last = now;
cfq_resort_rr_list(cfqq, 0);
}
- cfq_schedule_dispatch(cfqd);
}
- if (cfq_crq_is_sync(crq))
+ if (sync)
crq->io_context->last_end_request = now;
+
+ /*
+ * If this is the active queue, check if it needs to be expired,
+ * 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))
+ cfq_slice_expired(cfqd, 0);
+ else if (sync && RB_EMPTY(&cfqq->sort_list)) {
+ if (!cfq_arm_slice_timer(cfqd, cfqq))
+ cfq_schedule_dispatch(cfqd);
+ }
+ }
}
static struct request *
@@ -2106,11 +2145,8 @@
* only expire and reinvoke request handler, if there are
* other queues with pending requests
*/
- if (!cfqd->busy_queues) {
- cfqd->idle_slice_timer.expires = min(now + cfqd->cfq_slice_idle, cfqq->slice_end);
- add_timer(&cfqd->idle_slice_timer);
+ if (!cfqd->busy_queues)
goto out_cont;
- }
/*
* not expired and it has a request pending, let it dispatch