From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754604AbdBNQTt (ORCPT ); Tue, 14 Feb 2017 11:19:49 -0500 Received: from mga05.intel.com ([192.55.52.43]:60375 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753584AbdBNQTl (ORCPT ); Tue, 14 Feb 2017 11:19:41 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,161,1484035200"; d="scan'208";a="933790132" From: Alexander Shishkin To: Peter Zijlstra Cc: Ingo Molnar , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , Borislav Petkov , Thomas Gleixner Subject: Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX In-Reply-To: <20170214135620.GN6500@twins.programming.kicks-ass.net> References: <20170214132416.26400-1-alexander.shishkin@linux.intel.com> <20170214132416.26400-2-alexander.shishkin@linux.intel.com> <20170214135620.GN6500@twins.programming.kicks-ass.net> User-Agent: Notmuch/0.23.5 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Tue, 14 Feb 2017 18:17:30 +0200 Message-ID: <87d1eklpb9.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 Peter Zijlstra writes: > On Tue, Feb 14, 2017 at 03:24:15PM +0200, Alexander Shishkin wrote: >> At the moment, if VMX operation prevents PT tracing, the PMU will >> silently return success to the event scheduling code, which will >> track its 'on' time, etc. Instead, report failure so that perf >> core knows this event is not actually on. >> >> Signed-off-by: Alexander Shishkin >> Reported-by: Andi Kleen >> Fixes: 1c5ac21a0e ("perf/x86/intel/pt: Don't die on VMXON") >> --- >> arch/x86/events/intel/pt.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c >> index d92a60ef08..9372fa4549 100644 >> --- a/arch/x86/events/intel/pt.c >> +++ b/arch/x86/events/intel/pt.c >> @@ -1335,7 +1335,7 @@ static void pt_event_start(struct perf_event *event, int mode) >> struct pt_buffer *buf; >> >> if (READ_ONCE(pt->vmx_on)) >> - return; >> + goto fail_stop; >> >> buf = perf_aux_output_begin(&pt->handle, event); >> if (!buf) > > I'm not getting it; how does this matter to the time tracking in > event_sched_in() / event_sched_out() ? > > That looks at event->state == PERF_EVENT_STATE* > > This goto affects event->hw.state == PERF_HES_ > > The core assumes ->start() will _NOT_ fail. This is called by pmu::add(), which checks hw.state afterwards and if it finds HES_STOPPED, it returns an error, which event_sched_in() captures and keeps the event in INACTIVE state. Should I add a comment about it? Regards, -- Alex