Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755975AbcK2TcL (ORCPT ); Tue, 29 Nov 2016 14:32:11 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:56645 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751726AbcK2TcD (ORCPT ); Tue, 29 Nov 2016 14:32:03 -0500 Date: Tue, 29 Nov 2016 20:32:01 +0100 From: Peter Zijlstra To: "Liang, Kan" Cc: Stephane Eranian , "mingo@redhat.com" , LKML , Alexander Shishkin , "ak@linux.intel.com" , "Odzioba, Lukasz" Subject: Re: [PATCH] perf/x86: fix event counter update issue Message-ID: <20161129193201.GE3045@worktop.programming.kicks-ass.net> References: <1480361206-1702-1-git-send-email-kan.liang@intel.com> <20161129092520.GB3092@twins.programming.kicks-ass.net> <20161129173055.GP3092@twins.programming.kicks-ass.net> <37D7C6CF3E00A74B8858931C1DB2F07750CA4225@SHSMSX103.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37D7C6CF3E00A74B8858931C1DB2F07750CA4225@SHSMSX103.ccr.corp.intel.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 998 Lines: 25 On Tue, Nov 29, 2016 at 07:07:25PM +0000, Liang, Kan wrote: > > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c > > index a74a2dbc0180..cb8522290e6a 100644 > > --- a/arch/x86/events/intel/core.c > > +++ b/arch/x86/events/intel/core.c > > @@ -4034,7 +4034,7 @@ __init int intel_pmu_init(void) > > > > /* Support full width counters using alternative MSR range */ > > if (x86_pmu.intel_cap.full_width_write) { > > - x86_pmu.max_period = x86_pmu.cntval_mask; > > + x86_pmu.max_period = x86_pmu.cntval_mask >> 1; > > x86_pmu.perfctr = MSR_IA32_PMC0; > > pr_cont("full-width counters, "); > > } > > It doesn't work. > perf stat -x, -C1 -e cycles -- sudo taskset 0x2 ./loop 100000000000 > 18446743727217821696,,cycles,313837854019,100.00 > > delta 0xffffff8000001803 new 0x1804 prev 0xffffff8000000001 > > I guess we need at least x86_pmu.cntval_mask >> 2 to prevent > the sign flag set. Possible delta should be u64, as we know the counter cannot decrement.