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Wed, 06 May 2026 03:43:18 -0700 (PDT) Received: from [10.211.9.173] ([213.147.98.98]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-450524834eesm11178915f8f.4.2026.05.06.03.43.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 May 2026 03:43:18 -0700 (PDT) Message-ID: Date: Wed, 6 May 2026 04:43:17 -0600 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 v2] block: only read from sqe on initial invocation of blkdev_uring_cmd() To: Caleb Sander Mateos Cc: "linux-block@vger.kernel.org" References: <64e053e4-24aa-434d-9b35-794d3b292628@kernel.dk> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/5/26 9:32 AM, Caleb Sander Mateos wrote: > On Tue, May 5, 2026 at 12:38?AM Jens Axboe wrote: >> >> This passthrough helper currently only supports discards. Part of that >> command is the start and length, which is read from the SQE. It does >> so on every invocation, where it really should just make it stable >> on the first invocation. This avoids needing to copy the SQE upfront, >> as we only really need those two 8b values stored in our per-req >> payload. > > Maybe I'm missing something, but how does this avoid the SQE copy? > Won't io_uring_cmd_sqe_copy() still copy the SQE if the command issue > is delayed by links/drain/forced async or if the initial issue returns > EAGAIN? The code change looks fine to me, but I'm not sure I > understand the motivation. Because the alternative would be to copy it upfront and then using ->sqe would always be fine. But we can just ensure start/len are stable. The patch is about the latter, not adding any further copy avoidance. Yes if you use async or it's a link or drained, prep will always copy it. That's fine. -- Jens Axboe