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Wed, 22 Nov 2023 12:11:17 +0000 Date: Wed, 22 Nov 2023 12:11:16 +0000 Message-ID: <86il5uyom3.wl-maz@kernel.org> From: Marc Zyngier To: Mark Rutland Cc: Will Deacon , Huang Shijie , catalin.marinas@arm.com, suzuki.poulose@arm.com, broonie@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, anshuman.khandual@arm.com, robh@kernel.org, oliver.upton@linux.dev, patches@amperecomputing.com Subject: Re: [PATCH 0/4] arm64: an optimization for AmpereOne In-Reply-To: References: <20231122092855.4440-1-shijie@os.amperecomputing.com> <20231122094857.GA2959@willie-the-truck> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/29.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: mark.rutland@arm.com, will@kernel.org, shijie@os.amperecomputing.com, catalin.marinas@arm.com, suzuki.poulose@arm.com, broonie@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, anshuman.khandual@arm.com, robh@kernel.org, oliver.upton@linux.dev, patches@amperecomputing.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231122_041120_972104_5ACA7CC1 X-CRM114-Status: GOOD ( 21.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, 22 Nov 2023 11:40:09 +0000, Mark Rutland wrote: > > On Wed, Nov 22, 2023 at 09:48:57AM +0000, Will Deacon wrote: > > On Wed, Nov 22, 2023 at 05:28:51PM +0800, Huang Shijie wrote: > > > 0) Background: > > > We found that AmpereOne benefits from aggressive prefetches when > > > using 4K page size. > > > > We tend to shy away from micro-architecture specific optimisations in > > the arm64 kernel as they're pretty unmaintainable, hard to test properly, > > generally lead to bloat and add additional obstacles to updating our > > library routines. > > > > Admittedly, we have something for Thunder-X1 in copy_page() (disguised > > as ARM64_HAS_NO_HW_PREFETCH) but, frankly, that machine needed all the > > help it could get and given where it is today I suspect we could drop > > that code without any material consequences. > > > > So I'd really prefer not to merge this; modern CPUs should do better at > > copying data. It's copy_to_user(), not rocket science. > > I agree, and I'd also like to drop ARM64_HAS_NO_HW_PREFETCH. +1. Also, as the (most probably) sole user of this remarkable implementation, I hacked -rc2 to drop ARM64_HAS_NO_HW_PREFETCH. The result is that a kernel compilation job regressed by 0.4%, something that I consider being pure noise. If nobody beats me to it, I'll send the patch. M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel