[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 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -26,7 +26,7 @@ static const int cfq_back_penalty = 2;                /* penalty of a backwards seek */
 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 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
        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 @@ static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
         * 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 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
         */
        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 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
        } 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 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         */
        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 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 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 @@ cfq_forced_dispatch_cfqqs(struct list_head *list)
                }
                BUG_ON(!list_empty(&cfqq->fifo));
        }
+
        return dispatched;
 }
 
@@ -1146,7 +1152,8 @@ static int
 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 @@ cfq_dispatch_requests(request_queue_t *q, int force)
        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 @@ cfq_dispatch_requests(request_queue_t *q, int force)
                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 @@ static inline void changed_ioprio(struct cfq_io_context *cic)
 {
        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 @@ retry:
                 * 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 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 {
        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 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
                return 0;
 
        if (!cfqq)
-               return 1;
+               return 0;
 
        if (cfq_class_idle(cfqq))
                return 1;
@@ -1715,7 +1742,7 @@ static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
                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 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
                        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 @@ static void cfq_idle_slice_timer(unsigned long data)
                 * 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