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Fri, 24 Jul 2026 02:50:16 -0700 (PDT) Message-ID: Date: Fri, 24 Jul 2026 17:50:14 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] blk-wbt: Always change enable_state to MANUAL when setting latency To: Tang Yizhou Cc: yukuai@fygo.io, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, axboe@kernel.dk References: <20260717125021.88825-1-yizhou.tang@shopee.com> From: guzebing In-Reply-To: <20260717125021.88825-1-yizhou.tang@shopee.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/17/26 8:50 PM, Tang Yizhou wrote: > 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 = WBT_STATE_ON_DEFAULT, min_lat_nsec = 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") > Signed-off-by: Tang Yizhou > --- > block/blk-wbt.c | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) Indeed, this edge case was missed. Thanks for catching it. The patch looks good to me. Reviewed-by: Guzebing