From mboxrd@z Thu Jan 1 00:00:00 1970 From: jamal Subject: Re: fscked clock sources revisited Date: Mon, 30 Jul 2007 22:14:36 -0400 Message-ID: <1185848076.5162.39.camel@localhost> References: <1185844239.5162.17.camel@localhost> <20070730.183750.77058266.davem@davemloft.net> Reply-To: hadi@cyberus.ca Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Robert.Olsson@data.slu.se, shemminger@linux-foundation.org, kaber@trash.net To: David Miller Return-path: Received: from wx-out-0506.google.com ([66.249.82.233]:4771 "EHLO wx-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753032AbXGaCO6 (ORCPT ); Mon, 30 Jul 2007 22:14:58 -0400 Received: by wx-out-0506.google.com with SMTP id h31so1519054wxd for ; Mon, 30 Jul 2007 19:14:57 -0700 (PDT) In-Reply-To: <20070730.183750.77058266.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, 2007-30-07 at 18:37 -0700, David Miller wrote: > Relatively speaking, the acpi_pm numbers are at least consistent and > about as much as so as jiffies. Jiffies numbers are also possibly > better, at least in part, because of the decreased accuracy and errors > propagating. I am not sure jiffies gives innacurate results. It gives the best performance on the dual xeon i tested on, all the time. Very consistent. On its accuracy: I was able to validate it With pktgen generating traffic and some external hardware tool capturing the interpacket gaps etc. > tsc acts as expected, since every time your cpu changes power > management state (which it is going to do dynamically) the TSC > rates change and thus the accuracy goes into outer-space. Robert was saying he had even more bizare results with opteron given the NUMA nature. > There really isn't much that can be done by any of this. These issues > exist because of hardware limitations, nobody bothered to build > x86/x86_64 systems with a system wide TICK register that is both > impervious to cpu frequence scaling and also cheap to access. > > So the above is what we basically have to live with :-) That is a bummer. I am going to test with hpet when i get the chance and perhaps turn off all the other sources if nothing good comes out; i need my numbers ;-> cheers, jamal