Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751080AbVIWPVY (ORCPT ); Fri, 23 Sep 2005 11:21:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751082AbVIWPVY (ORCPT ); Fri, 23 Sep 2005 11:21:24 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:44162 "EHLO e32.co.us.ibm.com") by vger.kernel.org with ESMTP id S1751080AbVIWPVX (ORCPT ); Fri, 23 Sep 2005 11:21:23 -0400 Date: Fri, 23 Sep 2005 08:21:41 -0700 From: "Paul E. McKenney" To: Roman Zippel Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, mingo@elte.hu, akpm@osdl.org, george@mvista.com, johnstul@us.ibm.com Subject: Re: [ANNOUNCE] ktimers subsystem Message-ID: <20050923152141.GA29941@us.ibm.com> Reply-To: paulmck@us.ibm.com References: <20050919184834.1.patchmail@tglx.tec.linutronix.de> <1127342485.24044.600.camel@tglx.tec.linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1368 Lines: 33 On Fri, Sep 23, 2005 at 01:09:46AM +0200, Roman Zippel wrote: > On Thu, 22 Sep 2005, Thomas Gleixner wrote: [ . . . ] > > > The main difference between them is that the latter is user > > > programmable. > > > > wallclock is reprogrammable too and it introduces a bunch of horrible > > functions in posix-timers.c. grep for abs_list. I explained why its > > horrible already. > > I said _user_ programmable, wallclock time is usually NTP controlled. I believe Thomas is concerned about workloads that need a short-term stable timebase. For example, a process-control application might need to accurately measure a (say) 1500-millisecond time interval. Both user-programmability and NTP adjustments to a given timebase could destroy the needed measurement accuracy. Such a workload does not need the long-term tie to wallclock time that NTP provides, but it does need the accurate short-term timekeeping that NTP cannot provide -- NTP sacrifices short-term accuracy in order to adjust the clock as needed to gain long-term stability. Thomas, John, please jump in if I am missing the point here. Thanx, Paul - 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/