block, bfq: convert to use request_queue->async_depth

The default limits is unchanged, and user can configure async_depth now.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 44746f4c0b895e744a63da93f3e67892252196f8..b180ce5839518b2a36ad85864070eee0e3475279 100644 (file)
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7112,39 +7112,29 @@ void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
 static void bfq_depth_updated(struct request_queue *q)
 {
        struct bfq_data *bfqd = q->elevator->elevator_data;
-       unsigned int nr_requests = q->nr_requests;
+       unsigned int async_depth = q->async_depth;
 
        /*
-        * In-word depths if no bfq_queue is being weight-raised:
-        * leaving 25% of tags only for sync reads.
+        * By default:
+        *  - sync reads are not limited
+        * If bfqq is not being weight-raised:
+        *  - sync writes are limited to 75%(async depth default value)
+        *  - async IO are limited to 50%
+        * If bfqq is being weight-raised:
+        *  - sync writes are limited to ~37%
+        *  - async IO are limited to ~18
         *
-        * In next formulas, right-shift the value
-        * (1U<<bt->sb.shift), instead of computing directly
-        * (1U<<(bt->sb.shift - something)), to be robust against
-        * any possible value of bt->sb.shift, without having to
-        * limit 'something'.
+        * If request_queue->async_depth is updated by user, all limit are
+        * updated relatively.
         */
-       /* no more than 50% of tags for async I/O */
-       bfqd->async_depths[0][0] = max(nr_requests >> 1, 1U);
-       /*
-        * no more than 75% of tags for sync writes (25% extra tags
-        * w.r.t. async I/O, to prevent async I/O from starving sync
-        * writes)
-        */
-       bfqd->async_depths[0][1] = max((nr_requests * 3) >> 2, 1U);
+       bfqd->async_depths[0][1] = async_depth;
+       bfqd->async_depths[0][0] = max(async_depth * 2 / 3, 1U);
+       bfqd->async_depths[1][1] = max(async_depth >> 1, 1U);
+       bfqd->async_depths[1][0] = max(async_depth >> 2, 1U);
 
        /*
-        * In-word depths in case some bfq_queue is being weight-
-        * raised: leaving ~63% of tags for sync reads. This is the
-        * highest percentage for which, in our tests, application
-        * start-up times didn't suffer from any regression due to tag
-        * shortage.
+        * Due to cgroup qos, the allowed request for bfqq might be 1
         */
-       /* no more than ~18% of tags for async I/O */
-       bfqd->async_depths[1][0] = max((nr_requests * 3) >> 4, 1U);
-       /* no more than ~37% of tags for sync writes (~20% extra tags) */
-       bfqd->async_depths[1][1] = max((nr_requests * 6) >> 4, 1U);
-
        blk_mq_set_min_shallow_depth(q, 1);
 }
 
@@ -7365,6 +7355,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_queue *eq)
        blk_queue_flag_set(QUEUE_FLAG_DISABLE_WBT_DEF, q);
        wbt_disable_default(q->disk);
        blk_stat_enable_accounting(q);
+       q->async_depth = (q->nr_requests * 3) >> 2;
 
        return 0;