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Mon, 02 Sep 2019 23:00:13 -0700 (PDT) Date: Mon, 2 Sep 2019 23:00:11 -0700 From: Nathan Chancellor To: Will Deacon Subject: Re: [PATCH v5 03/10] arm64: atomics: avoid out-of-line ll/sc atomics Message-ID: <20190903060011.GA60737@archlinux-threadripper> References: <20190829154834.26547-1-will@kernel.org> <20190829154834.26547-4-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190829154834.26547-4-will@kernel.org> User-Agent: Mutt/1.12.1 (2019-06-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190902_230021_707754_6F2B1D26 X-CRM114-Status: GOOD ( 15.81 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, peterz@infradead.org, catalin.marinas@arm.com, ndesaulniers@google.com, Ard.Biesheuvel@arm.com, andrew.murray@arm.com, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Aug 29, 2019 at 04:48:27PM +0100, Will Deacon wrote: > From: Andrew Murray > > When building for LSE atomics (CONFIG_ARM64_LSE_ATOMICS), if the hardware > or toolchain doesn't support it the existing code will fallback to ll/sc > atomics. It achieves this by branching from inline assembly to a function > that is built with special compile flags. Further this results in the > clobbering of registers even when the fallback isn't used increasing > register pressure. > > Improve this by providing inline implementations of both LSE and > ll/sc and use a static key to select between them, which allows for the > compiler to generate better atomics code. Put the LL/SC fallback atomics > in their own subsection to improve icache performance. > > Signed-off-by: Andrew Murray > Signed-off-by: Will Deacon For some reason, this causes a clang built kernel to fail to boot in QEMU. There are no logs, it just never starts. I am off for the next two days so I am going to try to look into this but you might have some immediate ideas. https://github.com/ClangBuiltLinux/linux/issues/649 There is another weird failure that might be somewhat related but I have no idea. https://github.com/ClangBuiltLinux/linux/issues/648 Cheers, Nathan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel