From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935365Ab3E2W2Q (ORCPT ); Wed, 29 May 2013 18:28:16 -0400 Received: from mga02.intel.com ([134.134.136.20]:13728 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935302Ab3E2W2A (ORCPT ); Wed, 29 May 2013 18:28:00 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,766,1363158000"; d="scan'208";a="321585432" Subject: [v3][PATCH 1/4] perf/x86: only print PMU state when also WARN()'ing To: a.p.zijlstra@chello.nl Cc: mingo@redhat.com, paulus@samba.org, acme@ghostprotocols.net, tglx@linutronix.de, x86@kernel.org, linux-kernel@vger.kernel.org, Dave Hansen From: Dave Hansen Date: Wed, 29 May 2013 15:27:58 -0700 References: <20130529222756.25535229@viggo.jf.intel.com> In-Reply-To: <20130529222756.25535229@viggo.jf.intel.com> Message-Id: <20130529222758.60A34C05@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen intel_pmu_handle_irq() has a warning in it if it does too many loops. It is a WARN_ONCE(), but the perf_event_print_debug() call beneath it is unconditional. For the first warning, you get a nice backtrace and message, but subsequent ones just dump the PMU state with no leading messages. I doubt this is what was intended. This patch will only print the PMU state when paired with the WARN_ON() text. It effectively open-codes WARN_ONCE()'s one-time-only logic. My suspicion is that the code really just wants to make sure we do not sit in the loop and spit out a warning for every loop iteration after the 100th. From what I've seen, this is very unlikely to happen since we also clear the PMU state. After this patch, instead of seeing the PMU state dumped each time, you will just see: [57494.894540] perf_event_intel: clearing PMU state on CPU#129 [57579.539668] perf_event_intel: clearing PMU state on CPU#10 [57587.137762] perf_event_intel: clearing PMU state on CPU#134 [57623.039912] perf_event_intel: clearing PMU state on CPU#114 [57644.559943] perf_event_intel: clearing PMU state on CPU#118 ... Signed-off-by: Dave Hansen --- linux.git-davehans/arch/x86/kernel/cpu/perf_event_intel.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff -puN arch/x86/kernel/cpu/perf_event_intel.c~debug-perf-hangs arch/x86/kernel/cpu/perf_event_intel.c --- linux.git/arch/x86/kernel/cpu/perf_event_intel.c~debug-perf-hangs 2013-05-29 15:10:18.909649305 -0700 +++ linux.git-davehans/arch/x86/kernel/cpu/perf_event_intel.c 2013-05-29 15:10:18.912649437 -0700 @@ -1188,8 +1188,12 @@ static int intel_pmu_handle_irq(struct p again: intel_pmu_ack_status(status); if (++loops > 100) { - WARN_ONCE(1, "perfevents: irq loop stuck!\n"); - perf_event_print_debug(); + static bool warned = false; + if (!warned) { + WARN(1, "perfevents: irq loop stuck!\n"); + perf_event_print_debug(); + warned = true; + } intel_pmu_reset(); goto done; } _