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+ --- block/blk-throttle.c | 9 +++------ 1 file 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
On Mon, Jul 08, 2019 at 06:29:57PM +0300, Konstantin Khlebnikov wrote:
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+
block/blk-throttle.c | 9 +++------ 1 file 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
Did you use a tiny iops limit to run into this?
thanks, -liubo
On 08.07.2019 22:08, Liu Bo wrote:
On Mon, Jul 08, 2019 at 06:29:57PM +0300, Konstantin Khlebnikov wrote:
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+
block/blk-throttle.c | 9 +++------ 1 file 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
Did you use a tiny iops limit to run into this?
Yep. 25 iops
also kernel built with HZ=250, this might be related
thanks, -liubo
On 08.07.2019 18:29, Konstantin Khlebnikov wrote:
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.
To be clear: this almost instantly kills entire machine - other cpus stuck at sending ipi.
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+
block/blk-throttle.c | 9 +++------ 1 file 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
On 7/8/19 9:29 AM, Konstantin Khlebnikov wrote:
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.
Applied, thanks. In the future, please break lines at 72 chars in commit messages, I fixed it up.
On 10.07.2019 17:00, Jens Axboe wrote:
On 7/8/19 9:29 AM, Konstantin Khlebnikov wrote:
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.
Applied, thanks. In the future, please break lines at 72 chars in commit messages, I fixed it up.
Ok, but Documentation/process/submitting-patches.rst and scripts/checkpatch.pl recommends 75 chars per line.
On 7/10/19 8:24 AM, Konstantin Khlebnikov wrote:
On 10.07.2019 17:00, Jens Axboe wrote:
On 7/8/19 9:29 AM, Konstantin Khlebnikov wrote:
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.
Applied, thanks. In the future, please break lines at 72 chars in commit messages, I fixed it up.
Ok, but Documentation/process/submitting-patches.rst and scripts/checkpatch.pl recommends 75 chars per line.
Huh, oh well. Not a big deal for me, line breaking is easily automated.
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