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 <t...@kernel.org>
---
block/blk-throttle.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 1080563..99e1e78 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -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],
--
1.8.1.4
--
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