From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751281AbWJEUhK (ORCPT ); Thu, 5 Oct 2006 16:37:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751280AbWJEUhK (ORCPT ); Thu, 5 Oct 2006 16:37:10 -0400 Received: from tomts43-srv.bellnexxia.net ([209.226.175.110]:1416 "EHLO tomts43-srv.bellnexxia.net") by vger.kernel.org with ESMTP id S1751279AbWJEUhI (ORCPT ); Thu, 5 Oct 2006 16:37:08 -0400 Date: Thu, 5 Oct 2006 16:31:45 -0400 From: Mathieu Desnoyers To: Steven Rostedt Cc: Daniel Walker , LKML , Ingo Molnar , Thomas Gleixner , Karim Yaghmour , Andrew Morton , Chris Wright , fche@redhat.com, Tom Zanussi Subject: Re: [RFC] The New and Improved Logdev (now with kprobes!) Message-ID: <20061005203145.GA30746@Krystal> References: <1160025104.6504.30.camel@localhost.localdomain> <20061005143133.GA400@Krystal> <20061005170132.GA11149@Krystal> <1160072999.6660.5.camel@c-67-180-230-165.hsd1.ca.comcast.net> <1160074147.6660.10.camel@c-67-180-230-165.hsd1.ca.comcast.net> <20061005201820.GA1865@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.4.32-grsec (i686) X-Uptime: 16:30:18 up 43 days, 17:38, 8 users, load average: 0.20, 0.20, 0.26 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt (rostedt@goodmis.org) wrote: > > On Thu, 5 Oct 2006, Mathieu Desnoyers wrote: > > > > > Just as a detail : LTTng traces NMI, which can happen on top of a > > xtime_lock. So yes, I have to consider the impact of this kind of lock when I > > choose my time source, which is currently a per architecture TSC read, > > or a read of the jiffies counter when the architecture does not have a > > synchronised TSC over the CPUs. This is abstracted in include/asm-*/ltt.h. > > > > I'm curious. How do you show the interactions between two CPUs when the > TSC isn't in sync? Using jiffies is not fast enough to know the order of > events that happen within usecs. > I shift the jiffies and OR that with a logical clock which increments atomically and is shared across the CPUs. It is slow and ugly, but it works. :) Mathieu > -- Steve > > > > I know it doesn't support dynamic ticks, I'm working on using the HRtimers > > instead, but I must make sure that the seqlock read will fail if it nests over > > a write seqlock. > > > > MAthieu > > > > OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg > > Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 > > OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68