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Tue, 06 Jan 2026 18:10:48 -0800 (PST) From: Jens Axboe To: Breno Leitao Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, tj@kernel.org, josef@toxicpanda.com, kernel-team@meta.com In-Reply-To: <20260106-blk_unlikely-v1-1-90fb556a6776@debian.org> References: <20260106-blk_unlikely-v1-1-90fb556a6776@debian.org> Subject: Re: [PATCH] blk-rq-qos: Remove unlikely() hints from QoS checks Message-Id: <176775184768.14145.3891847681300037489.b4-ty@kernel.dk> Date: Tue, 06 Jan 2026 19:10:47 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Mailer: b4 0.14.3 On Tue, 06 Jan 2026 06:26:57 -0800, Breno Leitao wrote: > The unlikely() annotations on QUEUE_FLAG_QOS_ENABLED checks are > counterproductive. Writeback throttling (WBT) might be enabled by > default, mainly because CONFIG_BLK_WBT_MQ defaults to 'y'. > > Branch profiling on Meta servers, which have WBT enabled, confirms 100% > misprediction rates on these checks. > > [...] Applied, thanks! [1/1] blk-rq-qos: Remove unlikely() hints from QoS checks commit: 7d121d701d58a92f26decb10da1d04a88b74519d Best regards, -- Jens Axboe