From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753681Ab0CRRzt (ORCPT ); Thu, 18 Mar 2010 13:55:49 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:56487 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753321Ab0CRRzs (ORCPT ); Thu, 18 Mar 2010 13:55:48 -0400 Subject: Re: [RFC][PATCH] Convert alpha to use clocksource From: john stultz To: Richard Henderson Cc: lkml , Thomas Gleixner , Ivan Kokshaysky , Matt Turner In-Reply-To: <4BA23974.5030503@twiddle.net> References: <1268877702-2236-1-git-send-email-johnstul@us.ibm.com> <4BA23974.5030503@twiddle.net> Content-Type: text/plain; charset="UTF-8" Date: Thu, 18 Mar 2010 10:55:23 -0700 Message-ID: <1268934923.1855.8.camel@work-vm> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2010-03-18 at 07:32 -0700, Richard Henderson wrote: > On 03/17/2010 07:01 PM, John Stultz wrote: > > 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. > > With 8 seconds or less between roll-overs, do you actually consider > this a continuous counter? I don't. I suggest this be left alone. The timekeeping code handles this (although the shift value I picked may need some adjustment - what is the expected counter freq range on alpha?). The ACPI PM counter which is very common on x86 is only 24 bits and rolls over in ~5 seconds. It works fine. However, I'm not maintaining the arch, and this patch isn't limiting the timekeeping core, so the call is really yours. I sent this out on a whim since it looked easy to do. However, while this change is totally optional, I suspect my suggestion about moving to the clockevents code is going to rise in importance. The triplicate timer code paths of non-converted, converted periodic and converted one-shot is difficult to follow. I'll try to find a good example of an easy conversion case (PIT on x86 is not it) and send it your way. thanks -john