From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 12503 invoked by alias); 19 Apr 2018 16:58:16 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 12490 invoked by uid 89); 19 Apr 2018 16:58:15 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.4 required=5.0 tests=AWL,BAYES_00,KAM_SHORT,RCVD_IN_DNSWL_NONE,SPF_HELO_PASS,SPF_PASS autolearn=ham version=3.3.2 spammy= X-HELO: EUR01-DB5-obe.outbound.protection.outlook.com Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=Szabolcs.Nagy@arm.com; Cc: nd@arm.com Subject: Re: aarch64: add HWCAP_ATOMICS to HWCAP_IMPORTANT To: sellcey@cavium.com, GNU C Library References: <1d8eb765-e147-534e-ed1e-daa8deb8d5a7@arm.com> <1524154114.12392.17.camel@cavium.com> From: Szabolcs Nagy Message-ID: Date: Thu, 19 Apr 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1;AM6PR08MB3287;7:B1UxaG2nPs131G6mbQPSH8Zmcm5ChfXTJK563RqnnSlLQg8yla5iKt3GDKJU79uSzNDNJ8fO2bSOgAuckJs7SvbjA7L5PEnTjHhGEmrbNOTGh3Bppn9Fal3yN6l+HSXr3+wWVsknCDkhNbrI+0O1UrEO6G3b4Fe7WPMiS0ZW1lJ/on3b2AOq4R+N8p4U9jMtdt5nd0ecGlhWo4Eyg99dBNKhg4Qk+eQd7yf67u8H+IJcUD1/uabx1gyTKFiSBxnu X-MS-Office365-Filtering-Correlation-Id: 5dae4b86-228b-4930-0e7c-08d5a616bb46 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Apr 2018 16:58:10.2027 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5dae4b86-228b-4930-0e7c-08d5a616bb46 X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR08MB3287 X-SW-Source: 2018-04/txt/msg00422.txt.bz2 On 19/04/18 17:08, Steve Ellcey wrote: > On Thu, 2018-04-19 at 12:51 +0100, Szabolcs Nagy wrote: >> This enables searching shared libraries in atomics/ when the hardware >> supports LSE atomics of armv8.1 so one can provide optimized variants >> of libraries in a portable way. >> >> LSE atomics does not affect library abi, the new instructions can >> interoperate with old ones. >> >> I'm not familiar with how this feature of the dynamic linker is used >> in practice by distros or others so comments are welcome. >> >> 2018-04-19  Szabolcs Nagy   >> >> * sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h >> (HWCAP_IMPORTANT): Add >> HWCAP_ATOMICS. > > I don't know if this is relavent or not but I checked in changes a few > months ago to use IFUNC in libatomic so that it could use LSE (or not) > depending on the aarch64 hardware it is running on.  So if a user is > just using libatomic calls then they don't need a separate library or a > sperate search path.  If they want their own libraries with versions > that do or do not use LSE directly (and don't want to use IFUNCs) then > this could still be needed/desired. > yeah, i mainly want to enable libpthread/libc with lse atomics, it's not practical to ifunc all pthread primitives and malloc in glibc, but the armv8.1 atomic instructions may give significant benefit so we want a way to use those in distros. > https://gcc.gnu.org/ml/gcc-patches/2017-12/msg00187.html > https://gcc.gnu.org/ml/gcc-patches/2017-12/msg00434.html > > Steve Ellcey > sellcey@cavium.com >