Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261883AbVEPUzo (ORCPT ); Mon, 16 May 2005 16:55:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261878AbVEPUyh (ORCPT ); Mon, 16 May 2005 16:54:37 -0400 Received: from e32.co.us.ibm.com ([32.97.110.130]:46579 "EHLO e32.co.us.ibm.com") by vger.kernel.org with ESMTP id S261880AbVEPUx5 (ORCPT ); Mon, 16 May 2005 16:53:57 -0400 Subject: Re: IA64 implementation of timesource for new time of day subsystem From: john stultz To: Christoph Lameter Cc: David Mosberger , lkml , Tim Schmielau , George Anzinger , albert@users.sourceforge.net, Ulrich Windl , Dominik Brodowski , Andi Kleen , paulus@samba.org, schwidefsky@de.ibm.com, keith maanthey , Chris McDermott , Max Asbock , mahuja@us.ibm.com, Nishanth Aravamudan , Darren Hart , "Darrick J. Wong" , Anton Blanchard , donf@us.ibm.com, mpm@selenic.com, benh@kernel.crashing.org, linux-ia64@vger.kernel.org In-Reply-To: References: <1116029796.26454.2.camel@cog.beaverton.ibm.com> <1116029872.26454.4.camel@cog.beaverton.ibm.com> <1116029971.26454.7.camel@cog.beaverton.ibm.com> <1116030058.26454.10.camel@cog.beaverton.ibm.com> <1116030139.26454.13.camel@cog.beaverton.ibm.com> <1116264858.26990.39.camel@cog.beaverton.ibm.com> <1116269136.26990.67.camel@cog.beaverton.ibm.com> <17032.62615.750699.18847@napali.hpl.hp.com> <1116273055.13867.5.camel@cog.beaverton.ibm.com> Content-Type: text/plain Date: Mon, 16 May 2005 13:53:44 -0700 Message-Id: <1116276824.13867.15.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.0.4 (2.0.4-4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2119 Lines: 50 On Mon, 2005-05-16 at 13:27 -0700, Christoph Lameter wrote: > On Mon, 16 May 2005, john stultz wrote: > > > > > No. I intend to preserve the existing functionality (and performance) of > > the current code. The current timeofday core should allow for this (as I > > described in my last mail), so really its just a matter of either me or > > someone else getting around to properly converting that arch with the > > help of the arch maintainer. Until the arch is really ready to use the > > new timeofday core, no changes are necessary. > > Its not an arch specific issue. The time sources need to have a field that > specifies that jitter protection is needed and there needs to be some > logic to implement it. Otherwise we have to develop special functions for > each timesource that deal with jitter protection. You've only pointed out two timesources that could want this (ITC and TSC), so I think its reasonable to do your jitter handling in the timesource driver. If there are other arches that have non hardware synced per-cpu counters, then it would be something to consider. > Function will make a > fastcall for the clocks that use jitter protection not possible and thus > timer access will slow down. I disagree. I already explained how this can be done via the arch_update_vsyscall_gtod() interface by special casing for this specific well known time source. > > What I'm trying to shake out, with Christoph's help, is any major > > limitations in the core timeofday code that would keep an arch from > > being able to use it. I feel Christoph's concerns have been addressed, > > but please let me know if you disagree. > > Please add jitter protection to the arch independent code. If more timesources need that functionality, then I'll be happy to. Until then it should stay in the ia64 specific itc driver and fastcall code. thanks -john - 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/