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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-bd4f4dea94bsm565057266b.33.2026.05.18.06.59.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 May 2026 06:59:55 -0700 (PDT) Message-ID: <166da921-77bd-422e-85af-ef67d6fccc42@gmail.com> Date: Mon, 18 May 2026 14:59:54 +0100 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 04/10] block: introduce dma map backed bio type To: Christoph Hellwig Cc: =?UTF-8?Q?Christian_K=C3=B6nig?= , Jens Axboe , Keith Busch , Sagi Grimberg , Alexander Viro , Christian Brauner , Andrew Morton , Sumit Semwal , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Nitesh Shetty , Kanchan Joshi , Anuj Gupta , Tushar Gohad , William Power , Phil Cayton , Jason Gunthorpe References: <646ecd6fde8d9e146cb051efb514deb27ce3883e.1777475843.git.asml.silence@gmail.com> <20260513081929.GD5477@lst.de> <24833f76-2289-4859-86d1-9215b11a1258@gmail.com> <4561c621-817c-46be-8ff0-0b557f6c819d@gmail.com> <20260518125713.GC5754@lst.de> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20260518125713.GC5754@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/18/26 13:57, Christoph Hellwig wrote: > On Mon, May 18, 2026 at 01:40:18PM +0100, Pavel Begunkov wrote: >>> When that is really a performance critical path then you can use the likely() and unlikely() macros to give the compiler the hint which one to prefer. >> >> That might be more penalising than placing them in the right order, >> and it might be fine as it's new and all that, but it's not a clear >> cut as it's definitely not created to be a slow path. > > Yes. Whatever the caller is using at a given time is the fast path here, > and dynamic branch prediction in modern cpus handles this really well. > >> TBH, not sure >> why we're bike shedding such things, is it somewhere in the code >> style? > > It makes reading the code annoying, so it better have a good reason. > Now for a single conditional it's not much of an issue, but these > things tend to pile up and then start to get really annoying. > Always write your code the most straight forward way unless you > have a good reason not to. For me, having the most common case first is more natural and readable, but I'm going to flip it just to avoid spending more time here. -- Pavel Begunkov