From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner+willy=40w.ods.org-S264236AbUGOBiA@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S264236AbUGOBiA (ORCPT <rfc822;willy@w.ods.org>);
	Wed, 14 Jul 2004 21:38:00 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264850AbUGOBh7
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Wed, 14 Jul 2004 21:37:59 -0400
Received: from e35.co.us.ibm.com ([32.97.110.133]:59589 "EHLO
	e35.co.us.ibm.com") by vger.kernel.org with ESMTP id S264236AbUGOBhz
	(ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 14 Jul 2004 21:37:55 -0400
Subject: Re: gettimeofday nanoseconds patch (makes it possible for the
	posix-timer functions to return higher accuracy)
From: john stultz <johnstul@us.ibm.com>
To: David Mosberger <davidm@hpl.hp.com>
Cc: Christoph Lameter <clameter@sgi.com>, george anzinger <george@mvista.com>,
       lkml <linux-kernel@vger.kernel.org>, ia64 <linux-ia64@vger.kernel.org>
In-Reply-To: <16629.56037.120532.779793@napali.hpl.hp.com>
References: <Pine.LNX.4.58.0407140940260.14704@schroedinger.engr.sgi.com>
	 <1089835776.1388.216.camel@cog.beaverton.ibm.com>
	 <Pine.LNX.4.58.0407141323530.15874@schroedinger.engr.sgi.com>
	 <1089839740.1388.230.camel@cog.beaverton.ibm.com>
	 <Pine.LNX.4.58.0407141703360.17055@schroedinger.engr.sgi.com>
	 <1089852486.1388.256.camel@cog.beaverton.ibm.com>
	 <16629.56037.120532.779793@napali.hpl.hp.com>
Content-Type: text/plain
Message-Id: <1089855319.1388.295.camel@cog.beaverton.ibm.com>
Mime-Version: 1.0
X-Mailer: Ximian Evolution 1.4.5 (1.4.5-7) 
Date: Wed, 14 Jul 2004 18:35:20 -0700
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 2004-07-14 at 18:16, David Mosberger wrote:
> >>>>> On Wed, 14 Jul 2004 17:48:06 -0700, john stultz <johnstul@us.ibm.com> said:
> 
>   John> Although you still have the issue w/ NTP adjustments being
>   John> ignored, but last time I looked at the time_interpolator code,
>   John> it seemed it was being ignored there too, so at least your not
>   John> doing worse then the ia64 do_gettimeofday(). [If I'm doing the
>   John> time_interpolator code a great injustice with the above,
>   John> someone please correct me]
> 
> The existing time-interpolator code for ia64 never lets time go
> backwards (in the absence of a settimeofday(), of course).  There is
> no need to special-case NTP.

I guess I don't understand then, from my looking over it I didn't see
where the time_interpolator_get_offset() is scaled back when NTP is
slewing the clock. It seems that while the time-interpolator code does
keep time from going backwards, it also inadvertently ends up
compensating for NTP slow down. Thus the slewing is not visible to
userspace. 

In order for this to happen, time_interpolator_get_offset() would need
to be scaled or capped as to that it would not return more then the
length of the *NTP adjusted tick* during an actual tick interval.

I may be missing something, so please let me know if I'm wrong.

thanks
-john