Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.19 266/271] blk-throttle: fix zero wait time for iops throttled group | Date | Wed, 24 Jul 2019 21:22:15 +0200 |
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From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
commit 3a10f999ffd464d01c5a05592a15470a3c4bbc36 upstream.
After commit 991f61fe7e1d ("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: 991f61fe7e1d ("Blk-throttle: reduce tail io latency when iops limit is enforced") Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- block/blk-throttle.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)
--- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -892,13 +892,10 @@ static bool tg_with_in_iops_limit(struct unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; u64 tmp; - jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw]; + jiffy_elapsed = 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_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
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