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>

1 files changed, 18 insertions, 63 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 28236f2cd908..9d6f04103f01 100644
--- 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);