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Wed, 29 Jan 2025 11:11:04 -0800 (PST) Message-ID: Date: Wed, 29 Jan 2025 19:11:23 +0000 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7/8] io_uring: cache io_kiocb->flags in variable To: Max Kellermann , axboe@kernel.dk, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250128133927.3989681-1-max.kellermann@ionos.com> <20250128133927.3989681-8-max.kellermann@ionos.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20250128133927.3989681-8-max.kellermann@ionos.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/28/25 13:39, Max Kellermann wrote: > This eliminates several redundant reads, some of which probably cannot > be optimized away by the compiler. Let's not, it hurts readability with no clear benefits. In most cases the compiler will be able to optimise it just where it matters, and in cold paths we're comparing the overhead of reading a cached variable with taking locks and doing indirect calls, and even then it'd likely need to be saved onto the stack and loaded back. The only place where it might be worth it is io_issue_sqe(), and even then I'd doubt it. -- Pavel Begunkov