Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965181AbVKVUwo (ORCPT ); Tue, 22 Nov 2005 15:52:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965182AbVKVUwn (ORCPT ); Tue, 22 Nov 2005 15:52:43 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:48104 "EHLO mx3.mail.elte.hu") by vger.kernel.org with ESMTP id S965181AbVKVUwn (ORCPT ); Tue, 22 Nov 2005 15:52:43 -0500 Date: Tue, 22 Nov 2005 21:52:00 +0100 From: Ingo Molnar To: Steven Rostedt Cc: Christopher Friesen , Fernando Lopez-Lezcano , linux-kernel@vger.kernel.org, "Paul E. McKenney" , "K.R. Foley" , Thomas Gleixner , pluto@agmk.net, john cooper , Benedikt Spranger , Daniel Walker , Tom Rini , George Anzinger , john stultz Subject: Re: test time-warps [was: Re: 2.6.14-rt13] Message-ID: <20051122205200.GA17151@elte.hu> References: <20051115090827.GA20411@elte.hu> <1132608728.4805.20.camel@cmn3.stanford.edu> <20051121221511.GA7255@elte.hu> <20051121221941.GA11102@elte.hu> <20051122111623.GA948@elte.hu> <1132681766.21797.10.camel@cmn3.stanford.edu> <43835D01.3020304@nortel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=AWL autolearn=disabled SpamAssassin version=3.0.3 0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 996 Lines: 25 * Steven Rostedt wrote: > > > Apparently that's the case. > > > > What about periodically re-syncing the TSCs on the cpus? Are they > > writeable? > > I believe you can reset them to zero, but I don't think you can set > them to anything else. I had to do something similar a few years ago, > and I don't have the specs in front of me, so this is coming straight > from memory. on a reasonably new CPU you ought to be able to set the 64-bit value - but that doesnt change the fundamental fact: we have no idea how much time has passed while we were in HLT. Especially with things like dyntick/noidle we could spend _alot_ of time in HLT, and the TSC could drift significantly. How do we know how much that is? Ingo - 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/