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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3997f9955fbsm4721360f8f.5.2025.03.22.03.08.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 22 Mar 2025 03:08:52 -0700 (PDT) Date: Sat, 22 Mar 2025 10:08:51 +0000 From: David Laight To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Jens Axboe , David Howells , Matthew Wilcox , Andrew Morton , Alexander Viro Subject: Re: [PATCH next 0/3] iov: Optimise user copies Message-ID: <20250322100851.39c9eb33@pumpkin> In-Reply-To: References: <20250321224557.3847-1-david.laight.linux@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 21 Mar 2025 16:35:52 -0700 Linus Torvalds wrote: > On Fri, 21 Mar 2025 at 15:46, David Laight wrote: > > > > The speculation barrier in access_ok() is expensive. > > > > The first patch removes the initial checks when reading the iovec[]. > > The checks are repeated before the actual copy. > > > > The second patch uses 'user address masking' if supported. > > > > The third removes a lot of code for single entry iovec[]. > > Ack, except I'd really like to see numbers for things that claim to > remove expensive stuff. Testing readv() of /dev/zero or writev() of /dev/null probably show most gain. I did do some allmodconfig builds and got no change, but I might have the lfence compiled out of access_ok(). In any case kernel builds are pretty much user space limited. David > > But yeah, the patches look sane. > > Linus