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Tue, 04 Feb 2025 11:45:29 -0800 (PST) Message-ID: <7d927254-6e75-43c3-be17-6e449395ff0d@kernel.dk> Date: Tue, 4 Feb 2025 12:45:29 -0700 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 7/8] io_uring: cache io_kiocb->flags in variable To: Pavel Begunkov , Max Kellermann , 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: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/4/25 5:07 AM, Pavel Begunkov wrote: > 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. Yep I'll drop it, thanks. -- Jens Axboe