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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Jul 2022 07:30:52.6659 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7763e1cb-4f79-4b79-eb17-08da64a19de2 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: VE1EUR03FT006.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR0802MB2603 Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Hello all, The regression affects the perf command "stat" used with the option "-D msecs, --delay msecs". The change was introduced in v5.18 and was backported up to v5.15.33 of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git. In v5.18, the behaviour of the affected option is described in tools/perf/Documentation/perf-stat.txt as follows: "After starting the program, wait msecs before measuring (-1: start with events disabled). This is useful to filter out the startup phase of the program, which is often very different." The program is expected to start without delay. The observed behaviour in v5.18 does not correspond, as demonstrated by the following experiments: time perf stat --delay 2000 --quiet sleep 2 v5.18 output: Events disabled Events enabled real    0m4.065s user    0m0.019s sys    0m0.028s v5.17 output: Events disabled Events enabled real    0m2.028s user    0m0.001s sys    0m0.008s perf stat --delay 2000 --quiet echo "marking" v5.18 output: Events disabled Events enabled marking v5.17 output: Events disabled marking Events enabled I think there are two behaviours that are valuable to maintain to enable two uses: (1) if no delay is specified, the program should start after counters are enabled, to prevent the unexpected behaviour that Thomas fixed with this change; (2) if delay is specified, the program should start before the delay is engaged. Two possible solutions are: (1) though conditionals; if delay > 0, start the workload, then call enable_counters, which will usleep for the delay; if no delay, then behaviour as it is in v5.18; (2) replace blocking usleep with asynchronous callback, if that exists in Linux, that enables counters after the delay. Any suggestions from more experienced Linux developers on which solution to pursue will be appreciated. Kind regards, Adrián.