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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Mar 2025 16:28:02.6331 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9bab3d5b-6acc-4682-b9b9-08dd5ff08785 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: AM2PEPF0001C709.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV1PR08MB10905 On 3/10/25 12:47, Peter Zijlstra wrote: > On Fri, Mar 07, 2025 at 08:22:45PM +0000, mark.barnett@arm.com wrote: >> @@ -9922,7 +9923,10 @@ static int __perf_event_overflow(struct perf_event *event, >> if (event->attr.alt_sample_period) { >> bool using_alt = hwc->using_alt_sample_period; >> u64 sample_period = (using_alt ? event->attr.sample_period >> - : event->attr.alt_sample_period); >> + : event->attr.alt_sample_period) >> + + (event->attr.jitter_alt_period >> + ? get_random_u32_below(2 << event->attr.jitter_alt_period) >> + : 0); > > So, ... this here is NMI context, right? Have you looked at the guts of > get_random_u32_below() ? > > I would strongly suggest you go do so. > Good catch. I think a pseudo-random generator would be fine here and it looks like the implementation of prandom is safe to use in an interrupt context. I can change to use that. >> >> hwc->sample_period = sample_period; >> hwc->using_alt_sample_period = !using_alt;