From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750987AbdBOIha (ORCPT ); Wed, 15 Feb 2017 03:37:30 -0500 Received: from mga01.intel.com ([192.55.52.88]:23703 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782AbdBOIh3 (ORCPT ); Wed, 15 Feb 2017 03:37:29 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,165,1484035200"; d="scan'208";a="44687531" From: Alexander Shishkin To: Arnaldo Carvalho de Melo Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , Borislav Petkov , Thomas Gleixner Subject: Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on In-Reply-To: <20170214174734.GC4458@kernel.org> References: <20170214132416.26400-1-alexander.shishkin@linux.intel.com> <20170214132416.26400-3-alexander.shishkin@linux.intel.com> <20170214174734.GC4458@kernel.org> User-Agent: Notmuch/0.23.5 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Wed, 15 Feb 2017 10:34:58 +0200 Message-ID: <87poijkg25.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 Arnaldo Carvalho de Melo writes: > Em Tue, Feb 14, 2017 at 03:24:16PM +0200, Alexander Shishkin escreveu: >> On systems where PT does not coexist with VMX, users get confused when >> PT turns up with no data because they forgot they're running a kvm >> session at the same time. >> >> This patch adds a preemptive check for any active VMX operations that >> will fail event creation. This does not provide any guarantees or >> protection against racing with a kvm starting in parallel, but is >> intended to serve as a hint for the user. If VMXON happens after an >> event had been created, the event will still produce an empty trace. >> >> Signed-off-by: Alexander Shishkin >> Reported-by: Andi Kleen > > Yeah, I saw that as well, and Andi told me about this limitation, so, > for quite a while now, everytime I need to test PT on the only machine I > have with it, I have to stop my kvm sessions :-\ > > Thanks for working on this! Well, we can't make the limitation go away. You'll still have to stop kvms to get any 'meaningful' PT data. Regards, -- Alex