From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751890Ab0CSKHO (ORCPT ); Fri, 19 Mar 2010 06:07:14 -0400 Received: from jurassic.park.msu.ru ([195.208.223.243]:54713 "EHLO jurassic.park.msu.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750949Ab0CSKHM (ORCPT ); Fri, 19 Mar 2010 06:07:12 -0400 Date: Fri, 19 Mar 2010 13:07:10 +0300 From: Ivan Kokshaysky To: john stultz Cc: Richard Henderson , lkml , Thomas Gleixner , Matt Turner Subject: Re: [RFC][PATCH] Convert alpha to use clocksource Message-ID: <20100319100710.GA938@jurassic.park.msu.ru> References: <1268877702-2236-1-git-send-email-johnstul@us.ibm.com> <4BA23974.5030503@twiddle.net> <1268934923.1855.8.camel@work-vm> <20100318214030.GA8934@jurassic.park.msu.ru> <1268950758.4171.51.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1268950758.4171.51.camel@localhost.localdomain> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 18, 2010 at 03:19:18PM -0700, john stultz wrote: > On Fri, 2010-03-19 at 00:40 +0300, Ivan Kokshaysky wrote: > > Yeah, that looks cool. I'm typing this on the 800MHz UP1500 running > > 2.6.34-rc1 plus your patch, and the timekeeping works fine so far. > > Nice! Thanks for testing! Another benefit that I forgot to mention, is > that NTP adjustments will be made directly against the counter, instead > of being made against the tick. This avoids possible small errors at > tick time if the intertick interval doesn't match the actual tick > length. > > > > Though, even after a glance over the clocksource code, I've not > > gotten yet to how one could estimate the "shift" value... > > Any hints? > > Yea, selecting a good shift is obnoxious. You want to pick the largest > value of shift, so that it can be finely adjusted by ntp, but that > creates large mult values, which can cause overflows for large cycle > intervals. > > A function to solve this was actually recently added, but simply I > forgot to use it. :P Understood. ;-) > I actually should rework the register function so you just give it a > clocksource and a freq and it sets up both mult and shift for you. > > > > And if I recall correctly, production alphas have been clocked > > in the range of 60-1250 MHz. > > Cool. The shift value I picked should be ok then. But below is an > updated version that uses the self-calculated method. Excellent. Thanks a lot! > >From 078e91d14cb5e82a3fab00cf74faf45f44336590 Mon Sep 17 00:00:00 2001 > From: John Stultz > Date: Wed, 17 Mar 2010 12:43:11 -0700 > Subject: [PATCH] Convert alpha to use clocksources instead of arch_gettimeoffset > > Alpha has a tsc like rpcc counter that it uses to manage time. > This can be converted to an actual clocksource instead of utilizing > the arch_gettimeoffset method that is really only there for legacy > systems with no continuous counter. > > Further cleanups could be made if alpha converted to the clockevent model. > > I've not tested or compiled this code. Any help from the maintainers would > be greatly appreciated > > CC: Thomas Gleixner > CC: Richard Henderson > CC: Ivan Kokshaysky > CC: Matt Turner > Signed-off-by: John Stultz Acked-by: Ivan Kokshaysky Tested-by: Ivan Kokshaysky Ivan.