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Commit 9e660acf authored by Tejun Heo's avatar Tejun Heo
Browse files

blk-throttle: make blk_throtl_bio() ready for hierarchy 



Currently, blk_throtl_bio() issues the passed in bio directly if it's
within limits of its associated tg (throtl_grp).  This behavior
becomes incorrect with hierarchy support as the bio should be
accounted to and throttled by the ancestor throtl_grps too.

This patch makes the direct issue path of blk_throtl_bio() to loop
until it reaches the top-level service_queue or gets throttled.  If
the former, the bio can be issued directly; otherwise, it gets queued
at the first layer it was above limits.

As tg->parent_sq is always the top-level service queue currently, this
patch in itself doesn't make any behavior differences.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
parent 2a12f0dc

block/blk-throttle.c

+20 −7
Original line number Diff line number Diff line
@@ -1239,12 +1239,16 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) 


	sq = &tg->service_queue;



	/* throtl is FIFO - if other bios are already queued, should queue */

	while (true) {

		/* throtl is FIFO - if bios are already queued, should queue */

		if (sq->nr_queued[rw])

		goto queue_bio;

			break;



		/* if above limits, break to queue */

		if (!tg_may_dispatch(tg, bio, NULL))

			break;



	/* Bio is with-in rate limit of group */

	if (tg_may_dispatch(tg, bio, NULL)) {

		/* within limits, let's charge and dispatch directly */

		throtl_charge_bio(tg, bio);



		/*
@@ -1259,10 +1263,19 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) 
		 * So keep on trimming slice even if bio is not queued.

		 */

		throtl_trim_slice(tg, rw);



		/*

		 * @bio passed through this layer without being throttled.

		 * Climb up the ladder.  If we''re already at the top, it

		 * can be executed directly.

		 */

		sq = sq->parent_sq;

		tg = sq_to_tg(sq);

		if (!tg)

			goto out_unlock;

	}



queue_bio:

	/* out-of-limit, queue to @tg */

	throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",

		   rw == READ ? 'R' : 'W',

		   tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],