| Message ID | 20220517134909.2910251-1-yukuai3@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [-next] blk-throttle: delay the setting of 'BIO_THROTTLED' to when throttle is done | expand |
On Tue, May 17, 2022 at 09:49:09PM +0800, Yu Kuai wrote: > commit 9f5ede3c01f9 ("block: throttle split bio in case of iops limit") > introduce a new problem, for example: > > [root@localhost ~]# echo "8:0 1024" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device > [root@localhost ~]# echo $$ > /sys/fs/cgroup/blkio/cgroup.procs > [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct & > [1] 620 > [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct & > [2] 626 > [root@localhost ~]# 1+0 records in > 1+0 records out > 10240 bytes (10 kB, 10 KiB) copied, 10.0038 s, 1.0 kB/s1+0 records in > 1+0 records out > > 10240 bytes (10 kB, 10 KiB) copied, 9.23076 s, 1.1 kB/s > -> the second bio is issued after 10s instead of 20s. > > This is because if some bios are already queued, current bio is queued > directly and the flag 'BIO_THROTTLED' is set. And later, when former > bios are dispatched, this bio will be dispatched without waiting at all, > this is due to tg_with_in_bps_limit() will return 0 if the flag is set. > > Instead of setting the flag when bio starts throttle, delay to when > throttle is done to fix the problem. > > Fixes: 9f5ede3c01f9 ("block: throttle split bio in case of iops limit") > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > --- > block/blk-throttle.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > index 447e1b8722f7..f952f2d942ff 100644 > --- a/block/blk-throttle.c > +++ b/block/blk-throttle.c > @@ -811,7 +811,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio, > unsigned int bio_size = throtl_bio_data_size(bio); > > /* no need to throttle if this bio's bytes have been accounted */ > - if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) { > + if (bps_limit == U64_MAX) { This way may double account bio size for re-entered split bio. > if (wait) > *wait = 0; > return true; > @@ -1226,8 +1226,10 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work) > > spin_lock_irq(&q->queue_lock); > for (rw = READ; rw <= WRITE; rw++) > - while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL))) > + while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL))) { > + bio_set_flag(bio, BIO_THROTTLED); > bio_list_add(&bio_list_on_stack, bio); > + } > spin_unlock_irq(&q->queue_lock); > > if (!bio_list_empty(&bio_list_on_stack)) { > @@ -2134,7 +2136,8 @@ bool __blk_throtl_bio(struct bio *bio) > } > break; > } > - > + /* this bio will be issued directly */ > + bio_set_flag(bio, BIO_THROTTLED); > /* within limits, let's charge and dispatch directly */ > throtl_charge_bio(tg, bio); Marking BIO_THROTTLED before throtle_charge_bio() causes the bio bytes not be charged. Another simple way is to compensate for previous extra bytes accounting, something like the following patch: diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 139b2d7a99e2..44773d2ba257 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -810,8 +810,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio, unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; unsigned int bio_size = throtl_bio_data_size(bio); - /* no need to throttle if this bio's bytes have been accounted */ - if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) { + if (bps_limit == U64_MAX) { if (wait) *wait = 0; return true; @@ -921,10 +920,8 @@ static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio) unsigned int bio_size = throtl_bio_data_size(bio); /* Charge the bio to the group */ - if (!bio_flagged(bio, BIO_THROTTLED)) { - tg->bytes_disp[rw] += bio_size; - tg->last_bytes_disp[rw] += bio_size; - } + tg->bytes_disp[rw] += bio_size; + tg->last_bytes_disp[rw] += bio_size; tg->io_disp[rw]++; tg->last_io_disp[rw]++; @@ -2125,6 +2122,20 @@ bool __blk_throtl_bio(struct bio *bio) if (sq->nr_queued[rw]) break; + /* + * re-entered bio has accounted bytes already, so try to + * compensate previous over-accounting. However, if new + * slice is started, just forget it + */ + if (bio_flagged(bio, BIO_THROTTLED)) { + unsigned int bio_size = throtl_bio_data_size(bio); + + if (tg->bytes_disp[rw] >= bio_size) + tg->bytes_disp[rw] -= bio_size; + if (tg->last_bytes_disp[rw] - bio_size) + tg->last_bytes_disp[rw] -= bio_size; + } + /* if above limits, break to queue */ if (!tg_may_dispatch(tg, bio, NULL)) { tg->last_low_overflow_time[rw] = jiffies; Thanks, Ming
在 2022/05/18 12:07, Ming Lei 写道: > On Tue, May 17, 2022 at 09:49:09PM +0800, Yu Kuai wrote: >> commit 9f5ede3c01f9 ("block: throttle split bio in case of iops limit") >> introduce a new problem, for example: >> >> [root@localhost ~]# echo "8:0 1024" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device >> [root@localhost ~]# echo $$ > /sys/fs/cgroup/blkio/cgroup.procs >> [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct & >> [1] 620 >> [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct & >> [2] 626 >> [root@localhost ~]# 1+0 records in >> 1+0 records out >> 10240 bytes (10 kB, 10 KiB) copied, 10.0038 s, 1.0 kB/s1+0 records in >> 1+0 records out >> >> 10240 bytes (10 kB, 10 KiB) copied, 9.23076 s, 1.1 kB/s >> -> the second bio is issued after 10s instead of 20s. >> >> This is because if some bios are already queued, current bio is queued >> directly and the flag 'BIO_THROTTLED' is set. And later, when former >> bios are dispatched, this bio will be dispatched without waiting at all, >> this is due to tg_with_in_bps_limit() will return 0 if the flag is set. >> >> Instead of setting the flag when bio starts throttle, delay to when >> throttle is done to fix the problem. >> >> Fixes: 9f5ede3c01f9 ("block: throttle split bio in case of iops limit") >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >> --- >> block/blk-throttle.c | 10 ++++++---- >> 1 file changed, 6 insertions(+), 4 deletions(-) >> >> diff --git a/block/blk-throttle.c b/block/blk-throttle.c >> index 447e1b8722f7..f952f2d942ff 100644 >> --- a/block/blk-throttle.c >> +++ b/block/blk-throttle.c >> @@ -811,7 +811,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio, >> unsigned int bio_size = throtl_bio_data_size(bio); >> >> /* no need to throttle if this bio's bytes have been accounted */ >> - if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) { >> + if (bps_limit == U64_MAX) { > > This way may double account bio size for re-entered split bio. Hi, Ming Yes, you are right, I forgot that... > > >> if (wait) >> *wait = 0; >> return true; >> @@ -1226,8 +1226,10 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work) >> >> spin_lock_irq(&q->queue_lock); >> for (rw = READ; rw <= WRITE; rw++) >> - while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL))) >> + while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL))) { >> + bio_set_flag(bio, BIO_THROTTLED); >> bio_list_add(&bio_list_on_stack, bio); >> + } >> spin_unlock_irq(&q->queue_lock); >> >> if (!bio_list_empty(&bio_list_on_stack)) { >> @@ -2134,7 +2136,8 @@ bool __blk_throtl_bio(struct bio *bio) >> } >> break; >> } >> - >> + /* this bio will be issued directly */ >> + bio_set_flag(bio, BIO_THROTTLED); >> /* within limits, let's charge and dispatch directly */ >> throtl_charge_bio(tg, bio); > > Marking BIO_THROTTLED before throtle_charge_bio() causes the bio > bytes not be charged. Yes, thanks for spotting this. > > Another simple way is to compensate for previous extra bytes accounting, > something like the following patch: > > > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > index 139b2d7a99e2..44773d2ba257 100644 > --- a/block/blk-throttle.c > +++ b/block/blk-throttle.c > @@ -810,8 +810,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio, > unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; > unsigned int bio_size = throtl_bio_data_size(bio); > > - /* no need to throttle if this bio's bytes have been accounted */ > - if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) { > + if (bps_limit == U64_MAX) { > if (wait) > *wait = 0; > return true; > @@ -921,10 +920,8 @@ static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio) > unsigned int bio_size = throtl_bio_data_size(bio); > > /* Charge the bio to the group */ > - if (!bio_flagged(bio, BIO_THROTTLED)) { > - tg->bytes_disp[rw] += bio_size; > - tg->last_bytes_disp[rw] += bio_size; > - } > + tg->bytes_disp[rw] += bio_size; > + tg->last_bytes_disp[rw] += bio_size; > > tg->io_disp[rw]++; > tg->last_io_disp[rw]++; > @@ -2125,6 +2122,20 @@ bool __blk_throtl_bio(struct bio *bio) > if (sq->nr_queued[rw]) > break; > > + /* > + * re-entered bio has accounted bytes already, so try to > + * compensate previous over-accounting. However, if new > + * slice is started, just forget it > + */ > + if (bio_flagged(bio, BIO_THROTTLED)) { > + unsigned int bio_size = throtl_bio_data_size(bio); > + > + if (tg->bytes_disp[rw] >= bio_size) > + tg->bytes_disp[rw] -= bio_size; > + if (tg->last_bytes_disp[rw] - bio_size) > + tg->last_bytes_disp[rw] -= bio_size; > + } > + If new slice is not started, then this should fix the problem. From what I can see, other than tg_conf_updated, new silce can start if there are still bio throttled: tg_may_dispatch if (!(tg->service_queue.nr_queued[rw])) throtl_start_new_slice Thus I think the change is ok. For the case in tg_conf_updated, I'll remove the throtl_start_new_slice() to fix a hung problem. I'll add this patch with this one in next version. Thanks, Kuai > /* if above limits, break to queue */ > if (!tg_may_dispatch(tg, bio, NULL)) { > tg->last_low_overflow_time[rw] = jiffies; > > Thanks, > Ming > > . >
diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 447e1b8722f7..f952f2d942ff 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -811,7 +811,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio, unsigned int bio_size = throtl_bio_data_size(bio); /* no need to throttle if this bio's bytes have been accounted */ - if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) { + if (bps_limit == U64_MAX) { if (wait) *wait = 0; return true; @@ -1226,8 +1226,10 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work) spin_lock_irq(&q->queue_lock); for (rw = READ; rw <= WRITE; rw++) - while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL))) + while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL))) { + bio_set_flag(bio, BIO_THROTTLED); bio_list_add(&bio_list_on_stack, bio); + } spin_unlock_irq(&q->queue_lock); if (!bio_list_empty(&bio_list_on_stack)) { @@ -2134,7 +2136,8 @@ bool __blk_throtl_bio(struct bio *bio) } break; } - + /* this bio will be issued directly */ + bio_set_flag(bio, BIO_THROTTLED); /* within limits, let's charge and dispatch directly */ throtl_charge_bio(tg, bio); @@ -2190,7 +2193,6 @@ bool __blk_throtl_bio(struct bio *bio) out_unlock: spin_unlock_irq(&q->queue_lock); - bio_set_flag(bio, BIO_THROTTLED); #ifdef CONFIG_BLK_DEV_THROTTLING_LOW if (throttled || !td->track_bio_latency)
commit 9f5ede3c01f9 ("block: throttle split bio in case of iops limit") introduce a new problem, for example: [root@localhost ~]# echo "8:0 1024" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device [root@localhost ~]# echo $$ > /sys/fs/cgroup/blkio/cgroup.procs [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct & [1] 620 [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct & [2] 626 [root@localhost ~]# 1+0 records in 1+0 records out 10240 bytes (10 kB, 10 KiB) copied, 10.0038 s, 1.0 kB/s1+0 records in 1+0 records out 10240 bytes (10 kB, 10 KiB) copied, 9.23076 s, 1.1 kB/s -> the second bio is issued after 10s instead of 20s. This is because if some bios are already queued, current bio is queued directly and the flag 'BIO_THROTTLED' is set. And later, when former bios are dispatched, this bio will be dispatched without waiting at all, this is due to tg_with_in_bps_limit() will return 0 if the flag is set. Instead of setting the flag when bio starts throttle, delay to when throttle is done to fix the problem. Fixes: 9f5ede3c01f9 ("block: throttle split bio in case of iops limit") Signed-off-by: Yu Kuai <yukuai3@huawei.com> --- block/blk-throttle.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)