cfq-iosched: minor updates

- Move the queue_new flag clear to when the queue is selected
- Only select the non-first queue in cfq_get_best_queue(), if there's
  a substantial difference between the best and first.
- Get rid of ->busy_rr
- Only select a close cooperator, if the current queue is known to take
  a while to "think".

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 28236f2cd908a72b3c51a01f69cbd689769a944a..9d6f04103f01ae965959bb8b791373ffb633b020 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -70,7 +70,6 @@ struct cfq_data {
         * rr list of queues with requests and the count of them
         */
        struct list_head rr_list[CFQ_PRIO_LISTS];
-       struct list_head busy_rr;
        struct list_head cur_rr;
        struct list_head idle_rr;
        unsigned long cur_rr_tick;
@@ -410,59 +409,18 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 static void cfq_resort_be_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                                int preempted)
 {
-       struct list_head *list, *n;
-       struct cfq_queue *__cfqq;
-       int add_tail = 0;
-
-       /*
-        * if cfqq has requests in flight, don't allow it to be
-        * found in cfq_set_active_queue before it has finished them.
-        * this is done to increase fairness between a process that
-        * has lots of io pending vs one that only generates one
-        * sporadically or synchronously
-        */
-       if (cfqq->dispatched)
-               list = &cfqd->busy_rr;
-       else if (cfqq->ioprio == (cfqd->cur_prio + 1) &&
-                cfq_cfqq_sync(cfqq) &&
-                (time_before(cfqd->prio_time, cfqq->service_last) ||
-                 cfq_cfqq_queue_new(cfqq) || preempted)) {
-               list = &cfqd->cur_rr;
-               add_tail = 1;
-       } else
-               list = &cfqd->rr_list[cfqq->ioprio];
-
-       if (!cfq_cfqq_sync(cfqq) || add_tail) {
-               /*
-                * async queue always goes to the end. this wont be overly
-                * unfair to writes, as the sort of the sync queue wont be
-                * allowed to pass the async queue again.
-                */
-               list_add_tail(&cfqq->cfq_list, list);
-       } else if (preempted || cfq_cfqq_queue_new(cfqq)) {
-               /*
-                * If this queue was preempted or is new (never been serviced),
-                * let it be added first for fairness but beind other new
-                * queues.
-                */
-               n = list;
-               while (n->next != list) {
-                       __cfqq = list_entry_cfqq(n->next);
-                       if (!cfq_cfqq_queue_new(__cfqq))
-                               break;
+       if (!cfq_cfqq_sync(cfqq))
+               list_add_tail(&cfqq->cfq_list, &cfqd->rr_list[cfqq->ioprio]);
+       else {
+               struct list_head *n = &cfqd->rr_list[cfqq->ioprio];
 
-                       n = n->next;
-               }
-               list_add(&cfqq->cfq_list, n);
-       } else {
                /*
                 * sort by last service, but don't cross a new or async
-                * queue. we don't cross a new queue because it hasn't been
-                * service before, and we don't cross an async queue because
-                * it gets added to the end on expire.
+                * queue. we don't cross a new queue because it hasn't
+                * been service before, and we don't cross an async
+                * queue because it gets added to the end on expire.
                 */
-               n = list;
-               while ((n = n->prev) != list) {
+               while ((n = n->prev) != &cfqd->rr_list[cfqq->ioprio]) {
                        struct cfq_queue *__c = list_entry_cfqq(n);
 
                        if (!cfq_cfqq_sync(__c) || !__c->service_last)
@@ -725,6 +683,7 @@ __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
                cfq_clear_cfqq_must_alloc_slice(cfqq);
                cfq_clear_cfqq_fifo_expire(cfqq);
                cfq_mark_cfqq_slice_new(cfqq);
+               cfq_clear_cfqq_queue_new(cfqq);
                cfqq->rr_tick = cfqd->cur_rr_tick;
        }
 
@@ -743,7 +702,6 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 
        cfq_clear_cfqq_must_dispatch(cfqq);
        cfq_clear_cfqq_wait_request(cfqq);
-       cfq_clear_cfqq_queue_new(cfqq);
 
        /*
         * store what was left of this slice, if the queue idled out
@@ -845,13 +803,15 @@ static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
 static struct cfq_queue *cfq_get_best_queue(struct cfq_data *cfqd)
 {
        struct cfq_queue *cfqq = NULL, *__cfqq;
-       sector_t best = -1, dist;
+       sector_t best = -1, first = -1, dist;
 
        list_for_each_entry(__cfqq, &cfqd->cur_rr, cfq_list) {
                if (!__cfqq->next_rq || !cfq_cfqq_sync(__cfqq))
                        continue;
 
                dist = cfq_dist_from_last(cfqd, __cfqq->next_rq);
+               if (first == -1)
+                       first = dist;
                if (dist < best) {
                        best = dist;
                        cfqq = __cfqq;
@@ -859,9 +819,11 @@ static struct cfq_queue *cfq_get_best_queue(struct cfq_data *cfqd)
        }
 
        /*
-        * Only async queue(s) available, grab first entry
+        * Only async queue(s) available, grab first entry. Do the same
+        * if the difference between the first and best isn't more than
+        * twice, to obey fairness.
         */
-       if (!cfqq)
+       if (!cfqq || (best && first != best && ((first / best) < 4)))
                cfqq = list_entry_cfqq(cfqd->cur_rr.next);
 
        return cfqq;
@@ -878,12 +840,6 @@ static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
                 * are spliced
                 */
                cfqq = cfq_get_best_queue(cfqd);
-       } else if (!list_empty(&cfqd->busy_rr)) {
-               /*
-                * If no new queues are available, check if the busy list has
-                * some before falling back to idle io.
-                */
-               cfqq = list_entry_cfqq(cfqd->busy_rr.next);
        } else if (!list_empty(&cfqd->idle_rr)) {
                /*
                 * if we have idle queues and no rt or be queues had pending
@@ -1004,7 +960,8 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
        /*
         * See if this prio level has a good candidate
         */
-       if (cfq_close_cooperator(cfqd, cfqq))
+       if (cfq_close_cooperator(cfqd, cfqq) &&
+           (sample_valid(cic->ttime_samples) && cic->ttime_mean > 2))
                return;
 
        cfq_mark_cfqq_must_dispatch(cfqq);
@@ -1184,7 +1141,6 @@ cfq_forced_dispatch(struct cfq_data *cfqd)
        for (i = 0; i < CFQ_PRIO_LISTS; i++)
                dispatched += cfq_forced_dispatch_cfqqs(&cfqd->rr_list[i]);
 
-       dispatched += cfq_forced_dispatch_cfqqs(&cfqd->busy_rr);
        dispatched += cfq_forced_dispatch_cfqqs(&cfqd->cur_rr);
        dispatched += cfq_forced_dispatch_cfqqs(&cfqd->idle_rr);
 
@@ -2174,7 +2130,6 @@ static void *cfq_init_queue(request_queue_t *q)
        for (i = 0; i < CFQ_PRIO_LISTS; i++)
                INIT_LIST_HEAD(&cfqd->rr_list[i]);
 
-       INIT_LIST_HEAD(&cfqd->busy_rr);
        INIT_LIST_HEAD(&cfqd->cur_rr);
        INIT_LIST_HEAD(&cfqd->idle_rr);
        INIT_LIST_HEAD(&cfqd->cic_list);