From 183daeb11de871b073515d14ec1e3bc0da79e038 Mon Sep 17 00:00:00 2001 From: Kemeng Shi Date: Mon, 5 Dec 2022 19:57:04 +0800 Subject: blk-throttle: correct calculation of wait time in tg_may_dispatch In C language, When executing "if (expression1 && expression2)" and expression1 return false, the expression2 may not be executed. For "tg_within_bps_limit(tg, bio, bps_limit, &bps_wait) && tg_within_iops_limit(tg, bio, iops_limit, &iops_wait))", if bps is limited, tg_within_bps_limit will return false and tg_within_iops_limit will not be called. So even bps and iops are both limited, iops_wait will not be calculated and is always zero. So wait time of iops is always ignored. Fix this by always calling tg_within_bps_limit and tg_within_iops_limit to get wait time for both bps and iops. Observed that: 1. Wait time in tg_within_iops_limit/tg_within_bps_limit need always be stored as wait argument is always passed. 2. wait time is stored to zero if iops/bps is limited otherwise non-zero is stored. Simpfy tg_within_iops_limit/tg_within_bps_limit by removing wait argument and return wait time directly. Caller tg_may_dispatch checks if wait time is zero to find if iops/bps is limited. Acked-by: Tejun Heo Signed-off-by: Kemeng Shi Link: https://lore.kernel.org/r/20221205115709.251489-5-shikemeng@huaweicloud.com Signed-off-by: Jens Axboe --- block/blk-throttle.c | 38 +++++++++++++------------------------- 1 file changed, 13 insertions(+), 25 deletions(-) (limited to 'block') diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 75010110d481..d5b7a2354ad7 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -822,17 +822,15 @@ static void tg_update_carryover(struct throtl_grp *tg) tg->carryover_ios[READ], tg->carryover_ios[WRITE]); } -static bool tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio, - u32 iops_limit, unsigned long *wait) +static unsigned long tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio, + u32 iops_limit) { bool rw = bio_data_dir(bio); unsigned int io_allowed; unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; if (iops_limit == UINT_MAX) { - if (wait) - *wait = 0; - return true; + return 0; } jiffy_elapsed = jiffies - tg->slice_start[rw]; @@ -842,21 +840,16 @@ static bool tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio, io_allowed = calculate_io_allowed(iops_limit, jiffy_elapsed_rnd) + tg->carryover_ios[rw]; if (tg->io_disp[rw] + 1 <= io_allowed) { - if (wait) - *wait = 0; - return true; + return 0; } /* Calc approx time to dispatch */ jiffy_wait = jiffy_elapsed_rnd - jiffy_elapsed; - - if (wait) - *wait = jiffy_wait; - return false; + return jiffy_wait; } -static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio, - u64 bps_limit, unsigned long *wait) +static unsigned long tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio, + u64 bps_limit) { bool rw = bio_data_dir(bio); u64 bytes_allowed, extra_bytes; @@ -865,9 +858,7 @@ static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio, /* no need to throttle if this bio's bytes have been accounted */ if (bps_limit == U64_MAX || bio_flagged(bio, BIO_BPS_THROTTLED)) { - if (wait) - *wait = 0; - return true; + return 0; } jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw]; @@ -880,9 +871,7 @@ static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio, bytes_allowed = calculate_bytes_allowed(bps_limit, jiffy_elapsed_rnd) + tg->carryover_bytes[rw]; if (tg->bytes_disp[rw] + bio_size <= bytes_allowed) { - if (wait) - *wait = 0; - return true; + return 0; } /* Calc approx time to dispatch */ @@ -897,9 +886,7 @@ static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio, * up we did. Add that time also. */ jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed); - if (wait) - *wait = jiffy_wait; - return false; + return jiffy_wait; } /* @@ -947,8 +934,9 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio, jiffies + tg->td->throtl_slice); } - if (tg_within_bps_limit(tg, bio, bps_limit, &bps_wait) && - tg_within_iops_limit(tg, bio, iops_limit, &iops_wait)) { + bps_wait = tg_within_bps_limit(tg, bio, bps_limit); + iops_wait = tg_within_iops_limit(tg, bio, iops_limit); + if (bps_wait + iops_wait == 0) { if (wait) *wait = 0; return true; -- cgit v1.2.3