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Thu, 29 Sep 2022 16:35:16 +0000 From: Wilco Dijkstra To: Noah Goldstein CC: 'GNU C Library' Subject: [PATCH v1 2/4] nptl: Continue use arch prefered atomic exchange in spinlock loop Thread-Topic: [PATCH v1 2/4] nptl: Continue use arch prefered atomic exchange in spinlock loop Thread-Index: AQHY1CANoluRyjGD8UiP17REKvYQ/A== Date: Thu, 29 Sep 2022 16:35:16 +0000 Message-ID: Accept-Language: en-GB, en-US Content-Language: en-GB X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: Authentication-Results-Original: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=arm.com; x-ms-traffictypediagnostic: AS4PR08MB7901:EE_|AS4PR08MB7686:EE_|AM7EUR03FT003:EE_|AS8PR08MB9743:EE_ X-MS-Office365-Filtering-Correlation-Id: 7a479606-c752-432b-b595-08daa238a010 x-checkrecipientrouted: true nodisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; X-Microsoft-Antispam-Message-Info-Original: dnMEhQMejNk6ew2DJa374pGYSZEC+Mv4kyUqpwdG+AdvEVOmpZBf/xzLvIcj6dQzHr1Va2LxhsdCUW62Nu2PUJXGar9vKEQf4oLZylAsJMge7SNlWM75TDhuvbjqgX9ZfRbpj5DT/Mk6nFsNmP44B1SApGqX9QQbyVV5+LLlRnroX+vxO+Gk8XMEK9SQDakvRgFDZQcvzwoauFdMY7PoqoCNZGtUc8l4tZTjed6LlxZ7Rs/D7asWwmVt6f4x/qev8KCnuqwOXnecjNbKIsFn7Ou52FEMCL8BiQenNRsQi9JYFPDHy053D4Wq2BWNHV9S2UihI7udY51uiRvt6OxgySCyzyzsmdlq9US0+wlN2aEL5LljoHu2b7CEdJN8hshC4tEzP8PVxqjeCbDufVEVmjtyeo6GQr2tV0E3ENmM92ePzcjlkqAQjQv7FKz7UKBK77mF+rHsNS8ddGJgAoGnnMwNobPtTlY71XfTngjn9EMd8qFut0VBIqNZkGtBZgVeh6BTTVFfF4KWNhawasKp1sJQEFinWUr8BNb1b+1wgagoMxLo1LTEP6y12eKAy6n1QHlsGl5pBtqaMcKZZxlaXC0RClA79vRx+cfE4zRPMmYYYqfuBQ7hko4mT7W8ijDLx0EbVHCq7M3voj1iZaYIK3gs8BNAbm5MO3rYSqxpOv5k4MB/ZzJO+v8hILxkrJzbrXcn9D3RXaH8ChYTq+euQtwkXsFlYAETDz/2WPT6X/J8f3hnpBBoZCyon3nGFqXUhkaHOW2p6bZfM4veBcwxnA== X-Forefront-Antispam-Report-Untrusted: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:AS4PR08MB7901.eurprd08.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(4636009)(366004)(346002)(396003)(136003)(376002)(39850400004)(451199015)(478600001)(38100700002)(38070700005)(66946007)(66476007)(66556008)(66446008)(186003)(64756008)(4326008)(41300700001)(6916009)(76116006)(91956017)(6506007)(9686003)(2906002)(7696005)(122000001)(8676002)(5660300002)(316002)(86362001)(52536014)(4744005)(8936002)(83380400001)(26005)(33656002)(71200400001)(55016003);DIR:OUT;SFP:1101; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Sep 2022 16:35:31.3039 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7a479606-c752-432b-b595-08daa238a010 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: AM7EUR03FT003.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB9743 X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,KAM_DMARC_NONE,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,TXREP,UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Hi Noah,=0A= =0A= Did you try building it both ways? I don't think this could ever compile:= =0A= =0A= + =A0if (__glibc_likely (pthread_spin_lock_grab_lock (lock, &val, 1)))=0A= =0A= and:=0A= =0A= +# define pthread_spin_lock_grab_lock(mem, val, c) \=0A= + atomic_compare_exchange_weak_acquire (lock, &val, 1))=0A= =0A= The define uses 'lock' and 'mem' inconsistently and the use of the macro=0A= expands into &&val...=0A= =0A= Apart from that there is the question whether we should keep the weird=0A= ATOMIC_EXCHANGE_USES_CAS setting - I have removed it in my atomic=0A= patch series since most targets appear confused as to what it means (so=0A= are likely to have the wrong setting). Also there is no evidence it is actu= ally=0A= faster. So using exchange in both cases is easier (and less error prone!).= =0A= =0A= Also you do realize that no matter how much you change this code, it=0A= won't make a difference on x86, right?=0A= =0A= Cheers,=0A= Wilco=