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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: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
This commit is contained in:
Tejun Heo 2013-05-14 13:52:38 -07:00
parent 2a12f0dcda
commit 9e660acffc
1 changed files with 20 additions and 7 deletions
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27
block/blk-throttle.c
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@ -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 */
if (sq->nr_queued[rw])
goto queue_bio;
while (true) {
/* throtl is FIFO - if bios are already queued, should queue */
if (sq->nr_queued[rw])
break;
/* Bio is with-in rate limit of group */
if (tg_may_dispatch(tg, bio, NULL)) {
/* if above limits, break to queue */
if (!tg_may_dispatch(tg, bio, NULL))
break;
/* 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);
goto out_unlock;
/*
* @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],