Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262256AbVAZADA (ORCPT ); Tue, 25 Jan 2005 19:03:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262248AbVAZACh (ORCPT ); Tue, 25 Jan 2005 19:02:37 -0500 Received: from gate.crashing.org ([63.228.1.57]:61129 "EHLO gate.crashing.org") by vger.kernel.org with ESMTP id S262240AbVAZAAl (ORCPT ); Tue, 25 Jan 2005 19:00:41 -0500 Subject: Re: [RFC][PATCH] new timeofday arch specific hooks (v. A2) From: Benjamin Herrenschmidt To: john stultz Cc: lkml , Tim Schmielau , George Anzinger , albert@users.sourceforge.net, Ulrich Windl , Christoph Lameter , Dominik Brodowski , David Mosberger , Andi Kleen , Paul Mackerras , schwidefsky@de.ibm.com, keith maanthey , Patricia Gaughen , Chris McDermott , Max Asbock , mahuja@us.ibm.com, Nishanth Aravamudan , Darren Hart , "Darrick J. Wong" , Anton Blanchard In-Reply-To: <1106694561.30884.52.camel@cog.beaverton.ibm.com> References: <1106607089.30884.10.camel@cog.beaverton.ibm.com> <1106607153.30884.12.camel@cog.beaverton.ibm.com> <1106620134.15850.3.camel@gaston> <1106694561.30884.52.camel@cog.beaverton.ibm.com> Content-Type: text/plain Date: Wed, 26 Jan 2005 10:53:47 +1100 Message-Id: <1106697227.5235.28.camel@gaston> Mime-Version: 1.0 X-Mailer: Evolution 2.0.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1533 Lines: 35 On Tue, 2005-01-25 at 15:09 -0800, john stultz wrote: > The performance is a concern, and right now there are issues (ntp_scale > being the top of the list) however I hope they can be resolved. Looking > at ppc64's do_gettimeofday() vs this implementation there we do have > more overhead, but maybe you could suggest how we can avoid some of it? I would suggest reclaculating the scale factor and offset for ntp adjustement regulary from the timer tick or so, not on each gettimeofday call. Also, I have some updates to the ppc64 implementation where I regulary update the pre-scale offset into the post-scale one so that the timebase-prescale substraction always gives a 32 bits number. I do that so my fast userland gettimeofday can be implemented more easily and more efficiently for 32 bits processes. I yet have to check how I can hook those things into your new scheme. > I still want to support vsyscall gettimeofday, although it does have to > be done on an arch-by-arch basis. It's likely the systemcfg data > structure can still be generated and exported. I'll look into it and see > what can be done. Well, since it only contains the prescale and postscale offsets and the scaling value, it only needs to be updated when they change, so a hook here would be fine. Ben. - 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/