From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754947AbaGIJT1 (ORCPT ); Wed, 9 Jul 2014 05:19:27 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:53008 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751268AbaGIJTZ (ORCPT ); Wed, 9 Jul 2014 05:19:25 -0400 Date: Wed, 9 Jul 2014 11:19:17 +0200 From: Peter Zijlstra To: kan.liang@intel.com Cc: andi@firstfloor.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH V4 1/2] perf ignore LBR and extra_regs. Message-ID: <20140709091917.GC9918@twins.programming.kicks-ass.net> References: <1404838181-3911-1-git-send-email-kan.liang@intel.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="69pVuxX8awAiJ7fD" Content-Disposition: inline In-Reply-To: <1404838181-3911-1-git-send-email-kan.liang@intel.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --69pVuxX8awAiJ7fD Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Jul 08, 2014 at 09:49:40AM -0700, kan.liang@intel.com wrote: > + /* > + * Access LBR MSR may cause #GP under certain circumstances. > + * E.g. KVM doesn't support LBR MSR > + * Check all LBT MSR here. > + * Disable LBR access if any LBR MSRs can not be accessed. > + */ > + if (x86_pmu.lbr_nr) { > + access = check_msr(x86_pmu.lbr_tos); > + for (i = 0; i < x86_pmu.lbr_nr; i++) { > + access &= check_msr(x86_pmu.lbr_from + i); > + access &= check_msr(x86_pmu.lbr_to + i); > + } > + if (!access) > + x86_pmu.lbr_nr = 0; > + } You _could_ write that as: if (x86_pmu.lbr_nr) { if (!check_msr(x86_pmu.lbr_tos)) x86_pmu.lbr_nr = 0; for (i = 0; i < x86_pmu.lbr_nr; i++) { if (!(check_msr(x86_pmu.lbr_from + i) && check_msr(x86_pmu.lbr_to + i))) x86_pmu.lbr_nr = 0; } } There is no point in checking any more MSRs after the first fail after all. --69pVuxX8awAiJ7fD Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJTvQkVAAoJEHZH4aRLwOS6XMMP/2pubbvOc4B03UMdcbE9Mh4O gDQ8a+GXZEE5wGvUi9ota4xxQ8YHaSkRRHO4/5H8xD0QC648ivkd4JVviJEfy8WU zsKgoSLq4IbVzmfRcH4gpA7T7EEdPYLhtzBuGhKdhiVk/vG6Ppeh3xOkI9wEd5sT NeNdaIGbsxuhmrqb0ey2szdZtNThSVWz+AWPh3ws9dx1rSbJP6fWATSGAUGy2EBW zsio10c7ilhQol4MSQUXWXEhoZtSRAX1HGNYUQ8LuTD6gzC8M/K+8Ps7gChJAZFO FqI1V8rmWKyPDOIbOWOWdGZYStOOkJuPLmSr+gV8KUFKGfQJ8Bzc9PjCzj/ShHdE Ki3cLn5dfneNiteu+CHEAa3LIlb8I7aA5jAzI8PX8uK9QOsq/9F2nd6YKNBgN6Wz DVXd64dRuSPYstFXQ9D05fErQzXLzilciOyEqkMit5y6hdj+tfhfhpqAXYYFgDMV 6+M1TXjh9xpdNFRm+zYx8Y3g4A3e9sYFW5w7OS2dTXkzjTi3WQYdv9jyzteRQEHL ljGo7P/qjgTXJpb29nxrl5/xBtXim1z398pXOxjM/dGUXklTZ89JQGaTdtGd77Wo wg8W1CiFtjspQxPYn48Aeb3zfkccnTns+hm36UPqGizrQkht10mK7HrRO24FdX0b WO0f6JKK11ZK9IcXYgHC =jHP2 -----END PGP SIGNATURE----- --69pVuxX8awAiJ7fD--