Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932611AbbDOS2v (ORCPT ); Wed, 15 Apr 2015 14:28:51 -0400 Received: from casper.infradead.org ([85.118.1.10]:37330 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756305AbbDOS2r (ORCPT ); Wed, 15 Apr 2015 14:28:47 -0400 Date: Wed, 15 Apr 2015 20:28:36 +0200 From: Peter Zijlstra To: Kan Liang Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, acme@infradead.org, eranian@google.com, andi@firstfloor.org Subject: Re: [PATCH V6 4/6] perf, x86: handle multiple records in PEBS buffer Message-ID: <20150415182836.GX23123@twins.programming.kicks-ass.net> References: <1428597466-8154-1-git-send-email-kan.liang@intel.com> <1428597466-8154-5-git-send-email-kan.liang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1428597466-8154-5-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 Content-Length: 755 Lines: 17 On Thu, Apr 09, 2015 at 12:37:44PM -0400, Kan Liang wrote: > The only way you can get a lot of collision is when you count the same > thing multiple times. But it is not a useful configuration. Not entirely true; I _think_ you can be unfortunate if you measure with a userspace only PEBS event along with either a kernel or unrestricted PEBS event. Imagine the event triggering and setting the overflow flag right before entering the kernel. Then all kernel side events will end up with multiple bits set. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/