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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jan 2023 18:07:39.2074 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5a411959-fa21-4b5c-bd74-08daf4c7e45a 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: VI1EUR03FT046.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAWPR08MB9830 X-Spam-Status: No, score=-5.0 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 Zack,=0A= =0A= > I'm surprised to hear you say that. To me, 16 seconds is an absurdly _lo= ng_=0A= > interval for use of hp-timing.h. For anything longer than a few tens of= =0A= > milliseconds, the overhead of two system calls is negligible, but both CP= U=0A= > frequency changes and getting descheduled in the middle of the=0A= > measurement become serious concerns. So it seems more appropriate to=0A= > me to use clock_gettime with a per-process or per-thread clock ID for=0A= > measurements on the scale of tens of seconds.=0A= =0A= On AArch64 the counter is absolutely solid - it's fixed frequency and syste= m=0A= wide monotonically increasing. So there are no issues with varying clock=0A= frequency or rescheduling to a different core, you get elapsed time at=0A= nanosecond accuracy.=0A= =0A= With such a high quality counter it seems a waste to allow it to overflow= =0A= after a short time when there is a simple way to avoid it. Note we could=0A= remove the volatile from the asm as that would allow more lifting of the=0A= cntfreq and start the FP division earlier.=0A= =0A= Cheers,=0A= Wilco=