在 2025/4/17 10:27, Ming Lei 写道:
On Thu, Apr 17, 2025 at 09:50:31AM +0800, Zizhi Wo wrote: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. This patch fixes the issue. And if the bps/iops limit was previously set to max and later changed to a smaller value, we may not update tg->[bytes/io]_disp to 0 in tg_update_carryover(). Relying solely on throtl_trim_slice() is not sufficient, which can lead to subsequent bio dispatches not behaving as expected. We should set tg->[bytes/io]_disp to 0 in non_carryover case. The same handling applies when nr_queued is 0. Fixes: 6cc477c36875 ("blk-throttle: carry over directly") Signed-off-by: Zizhi Wo <wozizhi@xxxxxxxxxx> --- block/blk-throttle.c | 33 +++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 91dab43c65ab..df9825eb83be 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -644,20 +644,39 @@ 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 * carryover_bytes/ios will be used to calculate new wait time under new * configuration. */ - if (bps_limit != U64_MAX) + if (bps_limit != U64_MAX) { *bytes = calculate_bytes_allowed(bps_limit, jiffy_elapsed) - tg->bytes_disp[rw]; - if (iops_limit != UINT_MAX) + tg->bytes_disp[rw] = -*bytes; + } else { + tg->bytes_disp[rw] = 0; + }It should be fine to do 'tg->bytes_disp[rw] = -*bytes;' directly because `*bytes` is initialized as zero.
Indeed, I didn't notice that the incoming bytes/io is initialized to 0. Thanks, Zizhi Wo
+ + 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->io_disp[rw] = -*ios; + } else { + tg->io_disp[rw] = 0; + }Same with above. Otherwise, this patch looks fine. thanks, Ming
