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Thu, 20 Aug 2026 09:15:20 -0700 (PDT) From: Tang Yizhou X-Google-Original-From: Tang Yizhou To: axboe@kernel.dk, guzebing1612@gmail.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai@fygo.io, Tang Yizhou Subject: [PATCH v2] blk-wbt: Always change enable_state to MANUAL when setting latency Date: Fri, 21 Aug 2026 00:15:14 +0800 Message-ID: <20260820161514.371181-1-yizhou.tang@shopee.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tang Yizhou Commit 1e56f30a73f3 ("block: Make WBT latency writes honor enable state") compares only the boolean enabled state in the no-op check. Writing the current latency value while WBT is in WBT_STATE_ON_DEFAULT is therefore still skipped, and enable_state is not changed to WBT_STATE_ON_MANUAL. A subsequent elevator switch to BFQ then disables WBT through wbt_disable_default(), silently discarding the explicit sysfs setting: # enable_state =3D WBT_STATE_ON_DEFAULT, min_lat_nsec =3D 2000000 echo 2000 > /sys/block/nullb0/queue/wbt_lat_usec # skipped as a no-op echo bfq > /sys/block/nullb0/queue/scheduler cat /sys/block/nullb0/queue/wbt_lat_usec # 0, WBT disabled Skip the update only if the stored latency matches and enable_state already equals the exact target state: WBT_STATE_ON_MANUAL for a non-zero value, WBT_STATE_OFF_MANUAL for zero. A write that passes the check then reaches wbt_set_min_lat(), which performs the actual transition to the MANUAL state. Rename the helper to wbt_lat_changed() to improve readability. Fixes: 1e56f30a73f3 ("block: Make WBT latency writes honor enable state") Reviewed-by: Yu Kuai Reviewed-by: Guzebing Signed-off-by: Tang Yizhou Reviewed-by: Tao Cui --- v2: Pick Yuai and Guzebing's Reviewed-by tag. block/blk-wbt.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/block/blk-wbt.c b/block/blk-wbt.c index 953d400fd013..4f12a064286e 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -813,7 +813,14 @@ static void wbt_queue_depth_changed(struct rq_qos *rqo= s) wbt_update_limits(RQWB(rqos)); } =20 -static bool wbt_set_lat_changed(struct request_queue *q, u64 val) +/* + * Return true if writing @val would change the WBT state: + * 1) @val differs from the stored min_lat_nsec, or + * 2) @val matches, but enable_state is not the corresponding manual state + * (WBT_STATE_ON_MANUAL for non-zero @val, WBT_STATE_OFF_MANUAL for 0), + * so the write still has to update enable_state. + */ +static bool wbt_lat_changed(struct request_queue *q, u64 val) { struct rq_qos *rqos =3D wbt_rq_qos(q); struct rq_wb *rwb; @@ -825,7 +832,8 @@ static bool wbt_set_lat_changed(struct request_queue *q= , u64 val) if (rwb->min_lat_nsec !=3D val) return true; =20 - return rwb_enabled(rwb) !=3D !!val; + return rwb->enable_state !=3D + (val ? WBT_STATE_ON_MANUAL : WBT_STATE_OFF_MANUAL); } =20 static void wbt_exit(struct rq_qos *rqos) @@ -1021,7 +1029,7 @@ int wbt_set_lat(struct gendisk *disk, s64 val) val *=3D 1000ULL; =20 mutex_lock(&disk->rqos_state_mutex); - if (!wbt_set_lat_changed(q, val)) { + if (!wbt_lat_changed(q, val)) { mutex_unlock(&disk->rqos_state_mutex); goto out; } --=20 2.43.0