Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751140AbdGNUHw (ORCPT ); Fri, 14 Jul 2017 16:07:52 -0400 Received: from mga01.intel.com ([192.55.52.88]:40187 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751029AbdGNUHv (ORCPT ); Fri, 14 Jul 2017 16:07:51 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,359,1496127600"; d="scan'208";a="1195527813" From: Alexander Shishkin To: Vince Weaver , linux-kernel@vger.kernel.org Cc: Ingo Molnar , Peter Zijlstra , Stephane Eranian Subject: Re: perf: bisected sampling bug in Linux 4.11-rc1 In-Reply-To: References: User-Agent: Notmuch/0.23.7 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Fri, 14 Jul 2017 23:07:48 +0300 Message-ID: <87tw2ewzmz.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1197 Lines: 37 Vince Weaver writes: > I was tracking down some regressions in my perf_event_test testsuite. > Some of the tests broke in the 4.11-rc1 timeframe. > > I've bisected one of them, this report is about > tests/overflow/simul_oneshot_group_overflow > This test creates an event group containing two sampling events, set > to overflow to a signal handler (which disables and then refreshes the > event). > > On a good kernel you get the following: > Event perf::instructions with period 1000000 > Event perf::instructions with period 2000000 > fd 3 overflows: 946 (perf::instructions/1000000) > fd 4 overflows: 473 (perf::instructions/2000000) > Ending counts: > Count 0: 946379875 > Count 1: 946365218 > > With the broken kernels you get: > Event perf::instructions with period 1000000 > Event perf::instructions with period 2000000 > fd 3 overflows: 938 (perf::instructions/1000000) > fd 4 overflows: 318 (perf::instructions/2000000) > Ending counts: > Count 0: 946373080 > Count 1: 653373058 I'm not sure I'm seeing it (granted, it's a friday evening): is it the difference in overflow counts? Also, are they cpu or task bound? Regards, -- Alex