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| author | Konstantin Khlebnikov <khlebnikov@yandex-team.ru> | 2019-07-08 18:29:57 +0300 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2019-07-10 09:00:57 -0600 |
| commit | 3a10f999ffd464d01c5a05592a15470a3c4bbc36 (patch) | |
| tree | 84008b527c89f973b57d8f8a9fb1721a7004e4e7 /block/blk-throttle.c | |
| parent | 113ab72ed4794c193509a97d7c6d32a6886e1682 (diff) | |
| download | lwn-3a10f999ffd464d01c5a05592a15470a3c4bbc36.tar.gz lwn-3a10f999ffd464d01c5a05592a15470a3c4bbc36.zip | |
blk-throttle: fix zero wait time for iops throttled group
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>
Diffstat (limited to 'block/blk-throttle.c')
| -rw-r--r-- | block/blk-throttle.c | 9 |
1 files changed, 3 insertions, 6 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 9ea7c0ecad10..8ab6c8153223 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -881,13 +881,10 @@ 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 |