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[209.85.208.172]) by smtp.gmail.com with ESMTPSA id y25-20020ac24219000000b005114a0c56afsm1241553lfh.279.2024.02.27.08.34.56 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Feb 2024 08:34:56 -0800 (PST) Received: by mail-lj1-f172.google.com with SMTP id 38308e7fff4ca-2d23a22233fso46453731fa.2 for ; Tue, 27 Feb 2024 08:34:56 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCVIWsohJkr+6sj6CY/nD3QcB3GoRwT857U+QAnSM8AAjlaZJuMX8qsxhxt0mD6IHx/sR32YYTy1YIkVVJ5cJ5sBp0s= X-Received: by 2002:a05:6512:3d10:b0:513:3b3:e6f9 with SMTP id d16-20020a0565123d1000b0051303b3e6f9mr2440207lfv.26.1709051696282; Tue, 27 Feb 2024 08:34:56 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Tue, 27 Feb 2024 08:34:39 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [LSF/MM/BPF TOPIC] Measuring limits and enhancing buffered IO To: Kent Overstreet Cc: Al Viro , Matthew Wilcox , Luis Chamberlain , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm , Daniel Gomez , Pankaj Raghav , Jens Axboe , Dave Chinner , Christoph Hellwig , Chris Mason , Johannes Weiner Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: BEBE6100017 X-Stat-Signature: bt3enjqzpyhaj9ub71m77s5tt1c58f8s X-Rspam-User: X-HE-Tag: 1709051699-862953 X-HE-Meta: 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 eI3qpfBX DjcrRBhc3wE8GyJr6LOSORfiOG6aJxvtrm6vT5H6qXCjXFzqqtorFx/dTNANV9OxDGLcXAsmx+GaDaYE30RC/mgDswaPAr6PaK1zKGVH5CMdCTtmtZGpWWQem6rfsWFzvOO9jSNvHDGlE6VtJCwAYiFiMrAr96zlys0dVMpjxHRnnVMj0sdTx6HCVAGVXh5mrX58Z+K95lIxDbwDRTykw7rttfU7fbALH/CZ4XmsIuXyOgv3ciEUFTwzsJfIe+9tXP7HqZY8HKTsWcrh+g53N2c50Ew== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000094, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 26 Feb 2024 at 23:22, Kent Overstreet wrote: > > Only rough testing, but this is looking like around a 25% performance > increase doing 4k random reads on a 1G file with fio, 8 jobs, on my > Ryzen 5950x - 16.7M -> 21.4M iops, very roughly. fio's a pig and we're > only spending half our cpu time in the kernel, so the buffered read path > is actually getting 40% or 50% faster. > > So I'd say that's substantial. No, you're doing something wrong. The new fastread logic only triggers for reads <= 128 bytes, so you must have done some other major change (like built a kernel without the mitigations, and compared it to one with mitigations - that would easily be 25% depending on hardware). Linus