block: change the tag sync vs async restriction logic
Jens Axboe [Wed, 20 May 2009 06:54:31 +0000 (08:54 +0200)]
Make them fully share the tag space, but disallow async requests using
the last any two slots.

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

block/blk-barrier.c
block/blk-core.c
block/blk-tag.c
block/elevator.c
include/linux/blkdev.h

index 0ab81a0..0d98054 100644 (file)
@@ -218,7 +218,7 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
        } else
                skip |= QUEUE_ORDSEQ_PREFLUSH;
 
-       if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && q->in_flight)
+       if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
                rq = NULL;
        else
                skip |= QUEUE_ORDSEQ_DRAIN;
index 4906507..1c74840 100644 (file)
@@ -1815,7 +1815,7 @@ void blk_dequeue_request(struct request *rq)
         * the driver side.
         */
        if (blk_account_rq(rq))
-               q->in_flight++;
+               q->in_flight[rq_is_sync(rq)]++;
 }
 
 /**
index c260f7c..2e5cfeb 100644 (file)
@@ -336,7 +336,7 @@ EXPORT_SYMBOL(blk_queue_end_tag);
 int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 {
        struct blk_queue_tag *bqt = q->queue_tags;
-       unsigned max_depth, offset;
+       unsigned max_depth;
        int tag;
 
        if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
@@ -355,13 +355,16 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
         * to starve sync IO on behalf of flooding async IO.
         */
        max_depth = bqt->max_depth;
-       if (rq_is_sync(rq))
-               offset = 0;
-       else
-               offset = max_depth >> 2;
+       if (!rq_is_sync(rq) && max_depth > 1) {
+               max_depth -= 2;
+               if (!max_depth)
+                       max_depth = 1;
+               if (q->in_flight[0] > max_depth)
+                       return 1;
+       }
 
        do {
-               tag = find_next_zero_bit(bqt->tag_map, max_depth, offset);
+               tag = find_first_zero_bit(bqt->tag_map, max_depth);
                if (tag >= max_depth)
                        return 1;
 
index 9189200..ebee948 100644 (file)
@@ -546,7 +546,7 @@ void elv_requeue_request(struct request_queue *q, struct request *rq)
         * in_flight count again
         */
        if (blk_account_rq(rq)) {
-               q->in_flight--;
+               q->in_flight[rq_is_sync(rq)]--;
                if (blk_sorted_rq(rq))
                        elv_deactivate_rq(q, rq);
        }
@@ -685,7 +685,7 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
 
        if (unplug_it && blk_queue_plugged(q)) {
                int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
-                       - q->in_flight;
+                               - queue_in_flight(q);
 
                if (nrq >= q->unplug_thresh)
                        __generic_unplug_device(q);
@@ -823,7 +823,7 @@ void elv_completed_request(struct request_queue *q, struct request *rq)
         * request is released from the driver, io must be done
         */
        if (blk_account_rq(rq)) {
-               q->in_flight--;
+               q->in_flight[rq_is_sync(rq)]--;
                if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
                        e->ops->elevator_completed_req_fn(q, rq);
        }
@@ -838,7 +838,7 @@ void elv_completed_request(struct request_queue *q, struct request *rq)
                if (!list_empty(&q->queue_head))
                        next = list_entry_rq(q->queue_head.next);
 
-               if (!q->in_flight &&
+               if (!queue_in_flight(q) &&
                    blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
                    (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
                        blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
index 564445b..a967dd7 100644 (file)
@@ -404,7 +404,7 @@ struct request_queue
        struct list_head        tag_busy_list;
 
        unsigned int            nr_sorted;
-       unsigned int            in_flight;
+       unsigned int            in_flight[2];
 
        unsigned int            rq_timeout;
        struct timer_list       timeout;
@@ -511,6 +511,11 @@ static inline void queue_flag_clear_unlocked(unsigned int flag,
        __clear_bit(flag, &q->queue_flags);
 }
 
+static inline int queue_in_flight(struct request_queue *q)
+{
+       return q->in_flight[0] + q->in_flight[1];
+}
+
 static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
 {
        WARN_ON_ONCE(!queue_is_locked(q));