Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 1ab644bd authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Greg Kroah-Hartman
Browse files

blk-throttle: fix zero wait time for iops throttled group 



commit 3a10f999ffd464d01c5a05592a15470a3c4bbc36 upstream.

After commit 991f61fe ("Blk-throttle: reduce tail io latency when
iops limit is enforced") wait time could be zero even if group is
throttled and cannot issue requests right now. As a result
throtl_select_dispatch() turns into busy-loop under irq-safe queue
spinlock.

Fix is simple: always round up target time to the next throttle slice.

Fixes: 991f61fe ("Blk-throttle: reduce tail io latency when iops limit is enforced")
Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 91da712f

block/blk-throttle.c

+3 −6
Original line number Diff line number Diff line
@@ -892,13 +892,10 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio, 
	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;

	u64 tmp;



	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];



	/* Slice has just started. Consider one slice interval */

	if (!jiffy_elapsed)

		jiffy_elapsed_rnd = tg->td->throtl_slice;

	jiffy_elapsed = jiffies - tg->slice_start[rw];



	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);

	/* Round up to the next throttle slice, wait time must be nonzero */

	jiffy_elapsed_rnd = roundup(jiffy_elapsed + 1, tg->td->throtl_slice);



	/*

	 * jiffy_elapsed_rnd should not be a big value as minimum iops can be