From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261617AbVHAQ5Z (ORCPT ); Mon, 1 Aug 2005 12:57:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261398AbVHAQ5W (ORCPT ); Mon, 1 Aug 2005 12:57:22 -0400 Received: from atlrel6.hp.com ([156.153.255.205]:31402 "EHLO atlrel6.hp.com") by vger.kernel.org with ESMTP id S261303AbVHAQ5R (ORCPT ); Mon, 1 Aug 2005 12:57:17 -0400 From: Bjorn Helgaas To: Christoph Lameter Subject: Re: long delays (possibly infinite) in time_interpolator_get_counter Date: Mon, 1 Aug 2005 10:57:05 -0600 User-Agent: KMail/1.8.1 Cc: Alex Williamson , tony.luck@intel.com, linux-kernel@vger.kernel.org References: <200507292206.j6TM6w4k004594@agluck-lia64.sc.intel.com> <1122742054.28719.58.camel@localhost.localdomain> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200508011057.05802.bjorn.helgaas@hp.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 30 July 2005 12:10 pm, Christoph Lameter wrote: > On Sat, 30 Jul 2005, Alex Williamson wrote: > > > On Fri, 2005-07-29 at 16:31 -0700, Christoph Lameter wrote: > > > What you are dealing with is a machine that is using ITC as a time bases. > > > That is a special case. > > > > The default time source for ia64 systems is a "special case"? 4 > > socket and smaller boxes typically do not have any other time source. > > It is a special case because we typically use other time sources. Maybe you==SGI typically use other time sources, but most other ia64 boxes have synchronized ITCs. There's no reason such machines should have to use the slower and lower precision HPET. > If it is really synchronized then you can run with "nojitter" without any > issue. Then you wont have to deal with the cmpxchg and everything is fine. > But I suspect that the ITC are NOT truly synchronized (it has an > "offset" that may be nonzero right?) otherwise you would have used nojitter. And why should everyday users have to be concerned with "nojitter"? > Extra timer hardware is necessary to fix the ITC deficiency. You are at > the source of the problem. Fix the damn hardware to provide a standardized > synchronized clock or provide a truly synchronized ITC. The "ITC deficiency" is a platform design issue. Most small SMP platforms *do* synchronize the clocks of all processors. Obviously that's difficult on large boxes, and then you may need extra timers in the platform.