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Fri, 24 Nov 2023 13:47:25 +0000 From: Wilco Dijkstra To: Florian Weimer , Wilco Dijkstra via Libc-alpha Subject: Re: [PATCH] Improve performance of libc locks Thread-Topic: [PATCH] Improve performance of libc locks Thread-Index: AQHYrZ5WlKF2715S40mQdP77vhgIrLCLF3T2gAFCtv8= Date: Fri, 24 Nov 2023 13:47:25 +0000 Message-ID: References: <87h6lcbah7.fsf@oldenburg.str.redhat.com> In-Reply-To: <87h6lcbah7.fsf@oldenburg.str.redhat.com> 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: PAWPR08MB8982:EE_|AS2PR08MB8925:EE_|AM2PEPF0001C711:EE_|DB4PR08MB8199:EE_ X-MS-Office365-Filtering-Correlation-Id: 52275864-6789-4e7d-7ff6-08dbecf3eb14 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: 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 X-Forefront-Antispam-Report-Untrusted: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:PAWPR08MB8982.eurprd08.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(366004)(39860400002)(376002)(396003)(346002)(136003)(230922051799003)(64100799003)(1800799012)(186009)(451199024)(26005)(76116006)(66946007)(66556008)(33656002)(41300700001)(9686003)(71200400001)(86362001)(6506007)(7696005)(38070700009)(316002)(8676002)(122000001)(8936002)(64756008)(38100700002)(110136005)(91956017)(66476007)(66446008)(2906002)(52536014)(478600001)(5660300002)(83380400001)(55016003);DIR:OUT;SFP:1101; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Nov 2023 13:47:36.7317 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 52275864-6789-4e7d-7ff6-08dbecf3eb14 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: AM2PEPF0001C711.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB4PR08MB8199 X-Spam-Status: No, score=-1.5 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,KAM_DMARC_NONE,LIKELY_SPAM_BODY,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE,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 Florian,=A0=0A= =0A= > We already have SINGLE_THREAD_P checks around locking in several places.= =0A= > This makes the __libc_lock_lock check redudant in those cases.=A0 I=0A= > believe this was done deliberately because in many cases, we can also to= =0A= > skip cancellation handling at the same time.=0A= =0A= Yes, this is best for the most performance critical cases. However there ar= e lots of=0A= functions that use locks and many will improve with a single thread check a= t a =0A= higher level. You're right that would add extra checks in cases that are no= t=0A= performance critical.=0A= =0A= Maybe a solution would be to introduce __libc_lock_fast() or similar? That = way one=0A= can improve performance critical code easily without having to add special = fast=0A= paths. Today it would use SINGLE_THREAD_P, but it could potentially use RSE= Q in=0A= the future.=0A= =0A= > The rand performance issue could be addressed with a similar localized=0A= > change.=A0 I believe that would be far less controversial.=0A= =0A= I can send a patch that adds fast paths to rand() if that helps unblocking = this.=0A= =0A= Cheers,=0A= Wilco=0A=