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From: Kent Overstreet To: Linus Torvalds 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 Subject: Re: [LSF/MM/BPF TOPIC] Measuring limits and enhancing buffered IO Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 7AF3B40020 X-Stat-Signature: ntb9pwcjxctimhg6kojgfcou3moysq3y X-HE-Tag: 1709052441-8520 X-HE-Meta: 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 7QPjcN5a GwtUPbHA/LGcGw52BJhIHGBii5d/7lQgslydoldd/1/PhQW/RhqHBdUTZ9f6mholj1SsiM+XQLvUMl1QtJjPDrMO5ng== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Tue, Feb 27, 2024 at 08:34:39AM -0800, Linus Torvalds wrote: > 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). Like I replied to willy - the "4k" was a typo from force of habit, I was doing 64 byte random reads.