From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756065Ab2FFOle (ORCPT ); Wed, 6 Jun 2012 10:41:34 -0400 Received: from mga02.intel.com ([134.134.136.20]:29430 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753008Ab2FFOld (ORCPT ); Wed, 6 Jun 2012 10:41:33 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,352,1309762800"; d="scan'208";a="148899307" Date: Wed, 6 Jun 2012 07:41:32 -0700 From: Andi Kleen To: Peter Zijlstra Cc: Andi Kleen , linux-kernel@vger.kernel.org, eranian@google.com Subject: Re: [PATCH 5/5] perf, x86: Prefer RDPMC over RDMSR for reading counters Message-ID: <20120606144132.GJ28225@tassilo.jf.intel.com> References: <1338944211-28275-1-git-send-email-andi@firstfloor.org> <1338944211-28275-5-git-send-email-andi@firstfloor.org> <1338979579.2749.95.camel@twins> <20120606141644.GF28225@tassilo.jf.intel.com> <1338992472.2749.116.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1338992472.2749.116.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 06, 2012 at 04:21:12PM +0200, Peter Zijlstra wrote: > On Wed, 2012-06-06 at 07:16 -0700, Andi Kleen wrote: > > On Wed, Jun 06, 2012 at 12:46:19PM +0200, Peter Zijlstra wrote: > > > On Tue, 2012-06-05 at 17:56 -0700, Andi Kleen wrote: > > > > From: Andi Kleen > > > > > > > > RDPMC is much faster than RDMSR for reading performance counters, > > > > since it's not serializing. Use it if possible in the perf handler. > > > > > > > > Only tested on Sandy Bridge, so I only enabled it there so far. > > > > > > That's just stupid.. I took Vince's patch from a while back. > > > > What do you mean? It's significantly faster to read the counters this > > way, because it avoids serialization and other overhead. > > What I'm saying is you only enabling it for snb and being too lazy to > test anything else. Nor do I think its worth the conditional, all chips > we have PMU support for have rdpmc instructions. The reason I avoided it on everyone is that some old chips (NetBurst'ish I think) only were able to read the low 32bits through RDPMC. If you prefer I can enable it on all the P6 cores? I cannot test them all however. > > > Vince's patch only enabled it for user space I believe, This is for lowering > > the kernel PMI handler overhead. > > No, his patch did the kernel thing. Furthermore he actually tested it on > a bunch of machines. Ok. I wasn't aware of that. But it's not merged, what happened to ti? -Andi -- ak@linux.intel.com -- Speaking for myself only