From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mga11.intel.com ([192.55.52.93]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qLPlH-004LNZ-2y for linux-arm-kernel@lists.infradead.org; Mon, 17 Jul 2023 15:03:45 +0000 Date: Mon, 17 Jul 2023 18:03:32 +0300 From: Andy Shevchenko Subject: Re: [PATCH v3 1/5] lib/bitmap: add bitmap_{set,get}_value() Message-ID: References: <20230717113709.328671-1-glider@google.com> <20230717113709.328671-2-glider@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: 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+lwn-linux-arm-kernel=archive.lwn.net@lists.infradead.org List-Archive: To: Alexander Potapenko Cc: catalin.marinas@arm.com, will@kernel.org, pcc@google.com, andreyknvl@gmail.com, linux@rasmusvillemoes.dk, yury.norov@gmail.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, eugenis@google.com, syednwaris@gmail.com, william.gray@linaro.org, Arnd Bergmann On Mon, Jul 17, 2023 at 04:53:51PM +0200, Alexander Potapenko wrote: ... > > > I remember that this construction may bring horrible code on some architectures > > > with some version(s) of the compiler (*). > > > > Wow, even the trunk Clang and GCC seem to generate better code for > > your version of this line: https://godbolt.org/z/36Kqxhe6j > > Oh wait. > First, my Godbolt reproducer is incorrect, it is using sizeof(unsigned > long) instead of 8 * sizeof(unsigned long) for BITS_PER_LONG. Still slightly better. And note, that the same GENMASK() is used at the beginning of the function. Compiler actually might cache it. > > > To fix that I found an easy refactoring: > > > > > > map[index] &= ~(GENMASK(nbits, 0) << offset)); > > > > > Second, the line above should probably be: > map[index] &= ~(GENMASK(nbits - 1, 0) << offset)); > > , right? Yes. -- With Best Regards, Andy Shevchenko _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel