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[2620:137:e000::1:20]) by mx.google.com with ESMTP id u13-20020aa7db8d000000b004ad7204b7e4si11048109edt.500.2023.02.28.11.31.21; Tue, 28 Feb 2023 11:31:44 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229903AbjB1TWA convert rfc822-to-8bit (ORCPT + 99 others); Tue, 28 Feb 2023 14:22:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53878 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229470AbjB1TV6 (ORCPT ); Tue, 28 Feb 2023 14:21:58 -0500 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A33831A6 for ; Tue, 28 Feb 2023 11:21:56 -0800 (PST) Received: from pps.filterd (m0044010.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 31SIOUKo005371 for ; Tue, 28 Feb 2023 11:21:56 -0800 Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3p1f6hksvt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 28 Feb 2023 11:21:56 -0800 Received: from twshared18553.27.frc3.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.17; Tue, 28 Feb 2023 11:21:54 -0800 Received: by devbig932.frc1.facebook.com (Postfix, from userid 4523) id 93814172324C9; Tue, 28 Feb 2023 11:21:47 -0800 (PST) From: Song Liu To: CC: , Song Liu , Peter Zijlstra , Namhyung Kim Subject: [PATCH] perf: fix perf_event_context->time Date: Tue, 28 Feb 2023 11:21:45 -0800 Message-ID: <20230228192145.2120675-1-song@kernel.org> X-Mailer: git-send-email 2.30.2 X-FB-Internal: Safe X-Proofpoint-ORIG-GUID: X1EUv-MQOayHSKzHgXQ_39_8hTzy6Z68 X-Proofpoint-GUID: X1EUv-MQOayHSKzHgXQ_39_8hTzy6Z68 X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-02-28_17,2023-02-28_03,2023-02-09_01 X-Spam-Status: No, score=-2.3 required=5.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_LOW,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1759104419208909843?= X-GMAIL-MSGID: =?utf-8?q?1759104419208909843?= Time readers rely on perf_event_context->[time|timestamp|timeoffset] to get accurate time_enabled and time_running for an event. The difference between ctx->timestamp and ctx->time is the among of time when the context is not enabled. For cpuctx.ctx, time and timestamp should stay the same, however, it is not the case at the moment. To show this with drgn [1]: drgn 0.0.22 (using Python 3.8.6, elfutils 0.185, with libkdumpfile) For help, type help(drgn). ... >>> ctx = per_cpu_ptr(prog['pmu'].pmu_cpu_context, 0).ctx >>> ctx.timestamp * 1.0 / ctx.time (double)1.0385869134111765 >>> ctx->timestamp is about 4% larger than ctx.time. This issue causes time read by perf_event_read_local() goes back in some cases. Fix this by updating the condition for __update_context_time(ctx, false). Specifically, it should only be called when we enable EVENT_TIME for the ctx. [1] drgn: https://github.com/osandov/drgn Fixes: 09f5e7dc7ad7 ("perf: Fix perf_event_read_local() time") Cc: Peter Zijlstra (Intel) Cc: Namhyung Kim Signed-off-by: Song Liu Acked-by: Namhyung Kim --- kernel/events/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 380476a934e8..67478f43e26e 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3872,7 +3872,7 @@ ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type) if (likely(!ctx->nr_events)) return; - if (is_active ^ EVENT_TIME) { + if (!(is_active & EVENT_TIME)) { /* start ctx time */ __update_context_time(ctx, false); perf_cgroup_set_timestamp(cpuctx);