Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932548AbVJTWTe (ORCPT ); Thu, 20 Oct 2005 18:19:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932549AbVJTWTe (ORCPT ); Thu, 20 Oct 2005 18:19:34 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:65272 "EHLO hermes.mvista.com") by vger.kernel.org with ESMTP id S932548AbVJTWTd (ORCPT ); Thu, 20 Oct 2005 18:19:33 -0400 Message-ID: <435817F1.3000402@mvista.com> Date: Thu, 20 Oct 2005 15:19:29 -0700 From: George Anzinger Reply-To: george@mvista.com Organization: MontaVista Software User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050922 Fedora/1.7.12-1.3.1 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Daniel Walker Cc: Steven Rostedt , Thomas Gleixner , Ingo Molnar , ganzinger@mvista.com, linux-kernel@vger.kernel.org Subject: Re: Ktimer / -rt9 (+custom) monotonic_clock going backwards. References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1560 Lines: 33 Daniel Walker wrote: > On Thu, 20 Oct 2005, Steven Rostedt wrote: > >> >> Yes, but that shouldn't make a difference. NTP can slow down or speed up >> the clock, but it should never make it go backwards. Especially for a >> monotonic clock (as the name suggests). > > > It looks like if ntp_adj held a big negative number you might end up > with a smaller output . ntp_adj is signed too .. I don't know how > ntp_adj is set though . > > I thought I remember George Anzinger speculating that ntp could > cause the time to backwards , that's why I brought it up. Maybe if he's > read he can clue us in .. > I think John has changed this, but in the "old" code if ntp was correcting the clock such that less than TICK_NSEC was added on a tick, AND, the time was read just prior to this tick the get_offset code would return ~TICK_NSEC of offset which would mean that a read right after the tick might be less than the one just prior to the tick. The error, however, would be in the nanosecond area (no where near a second). Again, as I said, I think John has changed this in is code so that the get_offset equivalent is also ntp corrected, thus eliminating the small back step. > -- George Anzinger george@mvista.com HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/ - 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/