| Message ID | 156259979778.2486.6296077059654653057.stgit@buzz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | blk-throttle: fix zero wait time for iops throttled group | expand |
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.
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
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(-)