bfq: calculate shallow depths at init time

It doesn't change, so don't put it in the per-IO hot path.

Acked-by: Paolo Valente <paolo.valente@linaro.org>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index db38e88..0cd8aa8 100644 (file)
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -487,46 +487,6 @@ static struct request *bfq_choose_req(struct bfq_data *bfqd,
 }
 
 /*
- * See the comments on bfq_limit_depth for the purpose of
- * the depths set in the function.
- */
-static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
-{
-       bfqd->sb_shift = bt->sb.shift;
-
-       /*
-        * In-word depths if no bfq_queue is being weight-raised:
-        * leaving 25% of tags only for sync reads.
-        *
-        * In next formulas, right-shift the value
-        * (1U<<bfqd->sb_shift), instead of computing directly
-        * (1U<<(bfqd->sb_shift - something)), to be robust against
-        * any possible value of bfqd->sb_shift, without having to
-        * limit 'something'.
-        */
-       /* no more than 50% of tags for async I/O */
-       bfqd->word_depths[0][0] = max((1U<<bfqd->sb_shift)>>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->word_depths[0][1] = max(((1U<<bfqd->sb_shift) * 3)>>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.
-        */
-       /* no more than ~18% of tags for async I/O */
-       bfqd->word_depths[1][0] = max(((1U<<bfqd->sb_shift) * 3)>>4, 1U);
-       /* no more than ~37% of tags for sync writes (~20% extra tags) */
-       bfqd->word_depths[1][1] = max(((1U<<bfqd->sb_shift) * 6)>>4, 1U);
-}
-
-/*
  * Async I/O can easily starve sync I/O (both sync reads and sync
  * writes), by consuming all tags. Similarly, storms of sync writes,
  * such as those that sync(2) may trigger, can starve sync reads.
@@ -535,18 +495,11 @@ static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
  */
 static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
 {
-       struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
        struct bfq_data *bfqd = data->q->elevator->elevator_data;
-       struct sbitmap_queue *bt;
 
        if (op_is_sync(op) && !op_is_write(op))
                return;
 
-       bt = &tags->bitmap_tags;
-
-       if (unlikely(bfqd->sb_shift != bt->sb.shift))
-               bfq_update_depths(bfqd, bt);
-
        data->shallow_depth =
                bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)];
 
@@ -5126,6 +5079,55 @@ void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
        __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
 }
 
+/*
+ * See the comments on bfq_limit_depth for the purpose of
+ * the depths set in the function.
+ */
+static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
+{
+       bfqd->sb_shift = bt->sb.shift;
+
+       /*
+        * In-word depths if no bfq_queue is being weight-raised:
+        * leaving 25% of tags only for sync reads.
+        *
+        * In next formulas, right-shift the value
+        * (1U<<bfqd->sb_shift), instead of computing directly
+        * (1U<<(bfqd->sb_shift - something)), to be robust against
+        * any possible value of bfqd->sb_shift, without having to
+        * limit 'something'.
+        */
+       /* no more than 50% of tags for async I/O */
+       bfqd->word_depths[0][0] = max((1U<<bfqd->sb_shift)>>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->word_depths[0][1] = max(((1U<<bfqd->sb_shift) * 3)>>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.
+        */
+       /* no more than ~18% of tags for async I/O */
+       bfqd->word_depths[1][0] = max(((1U<<bfqd->sb_shift) * 3)>>4, 1U);
+       /* no more than ~37% of tags for sync writes (~20% extra tags) */
+       bfqd->word_depths[1][1] = max(((1U<<bfqd->sb_shift) * 6)>>4, 1U);
+}
+
+static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
+{
+       struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
+       struct blk_mq_tags *tags = hctx->sched_tags;
+
+       bfq_update_depths(bfqd, &tags->bitmap_tags);
+       return 0;
+}
+
 static void bfq_exit_queue(struct elevator_queue *e)
 {
        struct bfq_data *bfqd = e->elevator_data;
@@ -5547,6 +5549,7 @@ static struct elevator_type iosched_bfq_mq = {
                .requests_merged        = bfq_requests_merged,
                .request_merged         = bfq_request_merged,
                .has_work               = bfq_has_work,
+               .init_hctx              = bfq_init_hctx,
                .init_sched             = bfq_init_queue,
                .exit_sched             = bfq_exit_queue,
        },