From: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
To: Tao Cui <cuitao@kylinos.cn>
Cc: tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk,
cgroups@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [PATCH] blk-throttle: schedule parent dispatch in tg_flush_bios()
Date: Wed, 20 May 2026 21:33:21 +0900 [thread overview]
Message-ID: <ag2owaQQoigp_fSV@shinmob> (raw)
In-Reply-To: <20260520062420.1762788-1-cuitao@kylinos.cn>
On May 20, 2026 / 14:24, Tao Cui wrote:
> tg_flush_bios() schedules pending_timer on the child tg's own
> service_queue, which causes throtl_pending_timer_fn() to dispatch from
> the child's pending_tree. For leaf cgroups this tree is empty, so the
> timer fires and exits without dispatching the throttled bio.
>
> The throttled bio sits in the parent's pending_tree with disptime set
> to jiffies (THROTL_TG_CANCELING zeroes all dispatch times), but the
> parent's timer is never explicitly rescheduled. The bio only gets
> dispatched when the parent timer eventually fires at its previously
> scheduled expiry.
>
> Fix by calling throtl_schedule_next_dispatch(sq->parent_sq, true)
> instead, matching what tg_set_limit() already does. This forces the
> parent's dispatch cycle to run immediately and flush all canceling
> bios without waiting for a stale timer.
>
> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Hello Tao,
Trial runs of blktests CI for this patch caught the failure of test case
throtl/004 using scsi_debug device. I tried to recreate the failure manually.
I applied the patch on v7.1-rc4 kernel, and ran the test case and got the
result below. Is this failure expected?
# ./check throtl/004
throtl/004 (nullb) (delete disk while IO is throttled) [passed]
runtime 1.546s ... 1.332s
throtl/004 (sdebug) (delete disk while IO is throttled) [failed]
runtime 2.654s ... 2.435s
--- tests/throtl/004.out 2026-03-20 14:25:50.478000000 +0900
+++ /home/shin/Blktests/blktests/results/nodev_sdebug/throtl/004.out.bad 2026-05-20 21:26:14.470000000 +0900
@@ -1,3 +1,2 @@
Running throtl/004
-Input/output error
Test complete
next prev parent reply other threads:[~2026-05-20 12:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-20 6:24 [PATCH] blk-throttle: schedule parent dispatch in tg_flush_bios() Tao Cui
2026-05-20 12:33 ` Shin'ichiro Kawasaki [this message]
2026-05-20 14:20 ` Tao Cui
2026-05-20 23:39 ` Shin'ichiro Kawasaki
2026-05-21 2:54 ` Tao Cui
2026-05-21 4:54 ` Shin'ichiro Kawasaki
2026-05-21 7:54 ` Tao Cui
2026-05-21 9:04 ` Tao Cui
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