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Thu, 14 Mar 2024 14:27:12 +0000 Date: Thu, 14 Mar 2024 14:26:58 +0000 From: Szabolcs Nagy To: Adhemerval Zanella Netto , Wilco Dijkstra , 'GNU C Library' Subject: Re: [PATCH] AArch64: Check kernel version for SVE ifuncs Message-ID: References: <319a4afc-3841-4532-8350-be16e296c251@linaro.org> <44aeef4b-1044-4be8-9f35-e592a1c26080@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: LO4P123CA0494.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:1ab::13) To DB9PR08MB7179.eurprd08.prod.outlook.com (2603:10a6:10:2cc::19) MIME-Version: 1.0 X-MS-TrafficTypeDiagnostic: DB9PR08MB7179:EE_|AS4PR08MB7579:EE_|AMS0EPF000001B6:EE_|PAXPR08MB6654:EE_ X-MS-Office365-Filtering-Correlation-Id: a59cf77c-922a-45ff-8b23-08dc4432df1e 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:DB9PR08MB7179.eurprd08.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(376005)(1800799015);DIR:OUT;SFP:1101; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Mar 2024 14:27:26.1673 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a59cf77c-922a-45ff-8b23-08dc4432df1e 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: AMS0EPF000001B6.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAXPR08MB6654 X-Spam-Status: No, score=-5.4 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,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: The 03/14/2024 10:47, Adhemerval Zanella Netto wrote: > On 14/03/24 05:35, Szabolcs Nagy wrote: > > The 03/13/2024 16:55, Adhemerval Zanella Netto wrote: > >> On 13/03/24 16:25, Szabolcs Nagy wrote: > >>> The 03/13/2024 15:12, Adhemerval Zanella Netto wrote: > >> And I don't think __ASSUME_FAST_SVE would work well here, it means it > >> would always detect a good kernel even when running on a older one > > > > why? if it is set based on min supported kernel version then > > running on older kernel is a bug. if it can be overriden by > > a tunable then it is a user error if the tunable is wrong. > > > >> (I am not sure how usual this is). The minimum supported kernel > >> version can work to ensure that this check won't be necessary, but in > >> this case we won't really need this test anyway. > > > > you mean after min version is increased the check can be removed? > > i expect all __ASSUME* based on min linux version works like that > > and it's useful to have the __ASSUME exactly to be able to find > > which code can be removed after a min version increase. > > > > i don't know if distros actually adjust the min version in their > > glibc, i guess that would be risky if it should work in containers, > > so 6.2 min version is probably far in the future. > > All major distros I am aware of does not set --enable-kernel, so SVE > only will be selected either someone builds a glibc with > --enable-kernel=6.2 or when we raise the minimum version to 6.2. Not > a deal breaker, but the SVE routines will ended up not being actively > used for a long time. the __ASSUME would just gate the runtime version check, we would still do a kernel version check so sve will be used on new kernels, the __ASSUME is there so we dont forget to remove the check when the min version is high enough.