Hi,
在 2025/02/20 19:17, Ming Lei 写道:
When the current bio needs to be throttled because of bps limit, the wait
time for the extra bytes may be less than 1 jiffy, tg_within_bps_limit()
adds one extra 1 jiffy.
However, when taking roundup time into account, the extra 1 jiffy
may become not necessary, then bps limit becomes not accurate. This way
causes blktests throtl/001 failure in case of CONFIG_HZ_100=y.
Fix it by not adding the 1 jiffy in case that the roundup time can
cover it.
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Yu Kuai <yukuai3@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/blk-throttle.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 8d149aff9fd0..8348972c517b 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -729,14 +729,14 @@ static unsigned long tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
jiffy_wait = div64_u64(extra_bytes * HZ, bps_limit);
- if (!jiffy_wait)
- jiffy_wait = 1;
-
/*
* This wait time is without taking into consideration the rounding
* up we did. Add that time also.
*/
jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
+ if (!jiffy_wait)
+ jiffy_wait = 1;
Just wonder, will wait (0, 1) less jiffies is better than wait (0, 1)
more jiffies.
How about following changes?
Thanks,
Kuai
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 8d149aff9fd0..f8430baf3544 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -703,6 +703,7 @@ static unsigned long tg_within_bps_limit(struct
throtl_grp *tg, struct bio *bio,
u64 bps_limit)
{
bool rw = bio_data_dir(bio);
+ long long carryover_bytes;
long long bytes_allowed;
u64 extra_bytes;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
@@ -727,10 +728,11 @@ static unsigned long tg_within_bps_limit(struct
throtl_grp *tg, struct bio *bio,
/* Calc approx time to dispatch */
extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
- jiffy_wait = div64_u64(extra_bytes * HZ, bps_limit);
+ jiffy_wait = div64_u64_rem(extra_bytes * HZ, bps_limit,
carryover_bytes);
+ /* carryover_bytes is dispatched without waiting */
if (!jiffy_wait)
- jiffy_wait = 1;
+ tg->carryover_bytes[rw] -= carryover_bytes;
/*
* This wait time is without taking into consideration the rounding
+
return jiffy_wait;
}
