From f66cf69eb8765341bbeff0e92a7d0d2027f62452 Mon Sep 17 00:00:00 2001 From: Zizhi Wo Date: Thu, 17 Apr 2025 21:20:52 +0800 Subject: [PATCH] blk-throttle: Fix wrong tg->[bytes/io]_disp update in __tg_update_carryover() In commit 6cc477c36875 ("blk-throttle: carry over directly"), the carryover bytes/ios was be carried to [bytes/io]_disp. However, its update mechanism has some issues. In __tg_update_carryover(), we calculate "bytes" and "ios" to represent the carryover, but the computation when updating [bytes/io]_disp is incorrect. And if the sq->nr_queued is empty, we may not update tg->[bytes/io]_disp to 0 in tg_update_carryover(). We should set it to 0 in non carryover case. This patch fixes the issue. Fixes: 6cc477c36875 ("blk-throttle: carry over directly") Signed-off-by: Zizhi Wo Reviewed-by: Yu Kuai Reviewed-by: Ming Lei Link: https://lore.kernel.org/r/20250417132054.2866409-2-wozizhi@huaweicloud.com Signed-off-by: Jens Axboe --- block/blk-throttle.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index d6dd2e0478749..7437de947120e 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -644,6 +644,18 @@ static void __tg_update_carryover(struct throtl_grp *tg, bool rw, u64 bps_limit = tg_bps_limit(tg, rw); u32 iops_limit = tg_iops_limit(tg, rw); + /* + * If the queue is empty, carryover handling is not needed. In such cases, + * tg->[bytes/io]_disp should be reset to 0 to avoid impacting the dispatch + * of subsequent bios. The same handling applies when the previous BPS/IOPS + * limit was set to max. + */ + if (tg->service_queue.nr_queued[rw] == 0) { + tg->bytes_disp[rw] = 0; + tg->io_disp[rw] = 0; + return; + } + /* * If config is updated while bios are still throttled, calculate and * accumulate how many bytes/ios are waited across changes. And @@ -656,8 +668,8 @@ static void __tg_update_carryover(struct throtl_grp *tg, bool rw, if (iops_limit != UINT_MAX) *ios = calculate_io_allowed(iops_limit, jiffy_elapsed) - tg->io_disp[rw]; - tg->bytes_disp[rw] -= *bytes; - tg->io_disp[rw] -= *ios; + tg->bytes_disp[rw] = -*bytes; + tg->io_disp[rw] = -*ios; } static void tg_update_carryover(struct throtl_grp *tg) @@ -665,10 +677,8 @@ static void tg_update_carryover(struct throtl_grp *tg) long long bytes[2] = {0}; int ios[2] = {0}; - if (tg->service_queue.nr_queued[READ]) - __tg_update_carryover(tg, READ, &bytes[READ], &ios[READ]); - if (tg->service_queue.nr_queued[WRITE]) - __tg_update_carryover(tg, WRITE, &bytes[WRITE], &ios[WRITE]); + __tg_update_carryover(tg, READ, &bytes[READ], &ios[READ]); + __tg_update_carryover(tg, WRITE, &bytes[WRITE], &ios[WRITE]); /* see comments in struct throtl_grp for meaning of these fields. */ throtl_log(&tg->service_queue, "%s: %lld %lld %d %d\n", __func__, -- 2.50.1