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Commit f0635b8a authored by Jens Axboe's avatar Jens Axboe
Browse files

bfq: calculate shallow depths at init time 



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

Acked-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Reviewed-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 55141366

block/bfq-iosched.c

+50 −47
Original line number Diff line number Diff line
@@ -486,46 +486,6 @@ 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,
@@ -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,

	},