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([2620:10d:c092:600::1:f9be]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab6e47a7b1asm910914666b.31.2025.02.04.04.07.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Feb 2025 04:07:39 -0800 (PST) Message-ID: Date: Tue, 4 Feb 2025 12:07:49 +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 From: Pavel Begunkov 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 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/29/25 19:11, Pavel Begunkov wrote: > 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. Jens, I'd suggest to drop it out of the tree, for the reasons above. -- Pavel Begunkov