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[73.224.175.84]) by smtp.gmail.com with ESMTPSA id 00721157ae682-6f99fd1d5d8sm22523017b3.39.2025.02.11.10.44.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Feb 2025 10:44:19 -0800 (PST) Date: Tue, 11 Feb 2025 13:44:18 -0500 From: Yury Norov To: I Hsin Cheng Cc: anshuman.khandual@arm.com, arnd@arndb.de, linux-kernel@vger.kernel.org, jserv@ccns.ncku.edu.tw, skhan@linuxfoundation.org Subject: Re: [PATCH 1/2] uapi: Refactor __GENMASK() for speed-up Message-ID: References: <20250211162412.477655-1-richard120310@gmail.com> <20250211162412.477655-2-richard120310@gmail.com> 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-Disposition: inline In-Reply-To: On Tue, Feb 11, 2025 at 01:39:34PM -0500, Yury Norov wrote: > On Wed, Feb 12, 2025 at 12:24:11AM +0800, I Hsin Cheng wrote: > > The calculation of "((~_UL(0)) - (_UL(1) << (l)) + 1)" is to generate a > > bitmask with "l" trailing zeroes, which is equivalent to > > "(~_UL(0) << (l))". > > I used to think that GENMASK() is a compile-time macro. __GENMASK() is > not, but it has very limited usage through the kernel, all in the uapi. > > > Refactor the calculation so the number of arithmetic instruction will be > > reduced from 3 to 1. > > I'd like to look at it! Please share disassembly. > > > Signed-off-by: I Hsin Cheng > > --- > > Test is done to show the speed-up we can get from reducing the number of > > instruction. The test machine runs with 6.9.0-0-generic kernel on x86_64 > > architecture with processor AMD Ryzen 7 5700X3D 8-Core Processor. > > So you CC arm maintainers and provide tests against x86_64. Are your > improvements consistent for arm, power and other arches? > > Can you run bloat-o-meter against your change? Ah, sorry, overlooked you bloat-o-meter results in cover letter. Anyways, can you provide it for each patch individually?