From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752104Ab3BTVzn (ORCPT ); Wed, 20 Feb 2013 16:55:43 -0500 Received: from two.firstfloor.org ([193.170.194.197]:60985 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765Ab3BTVzm (ORCPT ); Wed, 20 Feb 2013 16:55:42 -0500 X-Greylist: delayed 445 seconds by postgrey-1.27 at vger.kernel.org; Wed, 20 Feb 2013 16:55:42 EST Date: Wed, 20 Feb 2013 22:48:16 +0100 From: Andi Kleen To: Stephane Eranian Cc: Andi Kleen , Jiri Olsa , LKML , Arnaldo Carvalho de Melo , Namhyung Kim , Corey Ashford , Frederic Weisbecker , Ingo Molnar , Paul Mackerras , Peter Zijlstra , David Ahern Subject: Re: [PATCH] perf x86: Change SandyBridge and IvyBrige instructions event to be precise Message-ID: <20130220214816.GC2928@two.firstfloor.org> References: <1361392794-16552-1-git-send-email-jolsa@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > I don't think it buys you much. People read too much into what > PEBS gives you. I can show you examples where PEBS > is worse than no PEBS. Nothing is perfect in sampling, but the precise instructions event is definitely better in a range of situations. It avoids a lot of shadow effects. I think it's a good choice for a lot of situations, although on Ivy Bridge without EventingRip the BB walking is still fairly expensive. It would be a good default for the "user only asks for instructions for sampling and nothing else" situation, especially on Haswell which has EventingRip. But that's not straight forward to detect. -Andi -- ak@linux.intel.com -- Speaking for myself only.