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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Mar 2025 20:28:29.8254 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7c11e61d-3132-41c7-2c37-08dd5db69f88 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: DU2PEPF00028D0D.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS2PR08MB8745 On 1/21/25 13:01, Leo Yan wrote: >> local64_set(&hwc->period_left, hwc->sample_period); >> >> + if (attr->alt_sample_period) { >> + hwc->sample_period = attr->alt_sample_period; >> + hwc->using_alt_sample_period = true; >> + } > > My understanding it sets a short sample window for the first period. > Would it initialize the `hwc->period_left` with the updated sample > period? > It sets the long period first: hwc->period_left is used to program the PMU when setting up the event, and hwc->sample_period is queued up as the next period to switch to. >> + >> + /* >> + * alt_sample_period cannot be used with freq >> + */ >> + if (attr->freq && attr->alt_sample_period) >> + goto err_ns; >> + > > It is good to validate parameters first. So move the checking before > the adjustment for the alt sample period. > Ack. Done. >> /* >> * We do not support PERF_SAMPLE_READ on inherited events unless >> * PERF_SAMPLE_TID is also selected, which allows inherited events to >> @@ -12763,9 +12788,19 @@ SYSCALL_DEFINE5(perf_event_open, >> if (attr.freq) { >> if (attr.sample_freq > sysctl_perf_event_sample_rate) >> return -EINVAL; >> + if (attr.alt_sample_period) >> + return -EINVAL; >> } else { >> if (attr.sample_period & (1ULL << 63)) >> return -EINVAL; >> + if (attr.alt_sample_period) { >> + if (!attr.sample_period) >> + return -EINVAL; >> + if (attr.alt_sample_period & (1ULL << 63)) >> + return -EINVAL; >> + if (attr.alt_sample_period == attr.sample_period) >> + attr.alt_sample_period = 0; > > In theory, the attr.alt_sample_period should be less than > attr.sample_period, right? > Added some validation for this.