Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751800AbYLEJer (ORCPT ); Fri, 5 Dec 2008 04:34:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751692AbYLEJeZ (ORCPT ); Fri, 5 Dec 2008 04:34:25 -0500 Received: from ozlabs.org ([203.10.76.45]:35033 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751404AbYLEJeW (ORCPT ); Fri, 5 Dec 2008 04:34:22 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18744.61830.572384.96322@cargo.ozlabs.ibm.com> Date: Fri, 5 Dec 2008 20:16:54 +1100 From: Paul Mackerras To: Peter Zijlstra Cc: Ingo Molnar , Thomas Gleixner , LKML , linux-arch@vger.kernel.org, Andrew Morton , Stephane Eranian , Eric Dumazet , Robert Richter , Arjan van de Veen , Peter Anvin , Steven Rostedt , David Miller Subject: Re: [patch 0/3] [Announcement] Performance Counters for Linux In-Reply-To: <1228464216.18899.18.camel@twins> References: <20081204225345.654705757@linutronix.de> <18744.29747.728320.652642@cargo.ozlabs.ibm.com> <20081205063131.GB12785@elte.hu> <20081205070329.GA30874@elte.hu> <1228461385.18899.13.camel@twins> <18744.57057.243817.407691@cargo.ozlabs.ibm.com> <1228464216.18899.18.camel@twins> X-Mailer: VM 8.0.9 under Emacs 22.2.1 (i486-pc-linux-gnu) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1051 Lines: 26 Peter Zijlstra writes: > On Fri, 2008-12-05 at 18:57 +1100, Paul Mackerras wrote: > > Peter Zijlstra writes: > > > > > So, while most people would not consider two consecutive read() ops to > > > be close or near the same time, due to preemption and such, that is > > > taken away by the fact that the counters are task local time based - so > > > preemption doesn't affect thing. Right? > > > > I'm sorry, I don't follow the argument here. What do you mean by > > "task local time based"? > > time only flows when the task is running. Right - but the monitored task is running while the monitoring task is running. So time is flowing for the monitored task between the two reads done by the monitoring task, meaning that you can't actually relate the two values you read with any precision. Paul. -- 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/