Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753720AbYAQCkR (ORCPT ); Wed, 16 Jan 2008 21:40:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751022AbYAQCkF (ORCPT ); Wed, 16 Jan 2008 21:40:05 -0500 Received: from tomts40.bellnexxia.net ([209.226.175.97]:45886 "EHLO tomts40-srv.bellnexxia.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751045AbYAQCkD (ORCPT ); Wed, 16 Jan 2008 21:40:03 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Aq4HAFZOjkdMROHU/2dsb2JhbACBWKxa Date: Wed, 16 Jan 2008 21:40:00 -0500 From: Mathieu Desnoyers To: john stultz Cc: Steven Rostedt , LKML , Ingo Molnar , Linus Torvalds , Andrew Morton , Peter Zijlstra , Christoph Hellwig , Gregory Haskins , Arnaldo Carvalho de Melo , Thomas Gleixner , Tim Bird , Sam Ravnborg , "Frank Ch. Eigler" , Steven Rostedt , Paul Mackerras , Daniel Walker Subject: Re: [RFC PATCH 16/22 -v2] add get_monotonic_cycles Message-ID: <20080117024000.GD2322@Krystal> References: <20080115220824.GB22242@Krystal> <20080116031730.GA2164@Krystal> <20080116145604.GB31329@Krystal> <1f1b08da0801161436k4a7ac1e3kd83590951e7bebb9@mail.gmail.com> <1200523867.6127.5.camel@localhost.localdomain> <1200536889.6127.52.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <1200536889.6127.52.camel@localhost.localdomain> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 21:38:35 up 74 days, 7:44, 5 users, load average: 1.15, 1.64, 1.09 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2365 Lines: 66 * john stultz (johnstul@us.ibm.com) wrote: > > On Wed, 2008-01-16 at 18:33 -0500, Steven Rostedt wrote: > > Thanks John for doing this! > > > > (comments imbedded) > > > > On Wed, 16 Jan 2008, john stultz wrote: > > > + int num = !cs->base_num; > > > + cycle_t offset = (now - cs->base[!num].cycle_base_last); > > > + offset &= cs->mask; > > > + cs->base[num].cycle_base = cs->base[!num].cycle_base + offset; > > > + cs->base[num].cycle_base_last = now; > > > > I would think that we would need some sort of barrier here. Otherwise, > > base_num could be updated before all the cycle_base. I'd expect a smp_wmb > > is needed. > > Hopefully addressed in the current version. > > > > > Index: monotonic-cleanup/kernel/time/timekeeping.c > > > =================================================================== > > > --- monotonic-cleanup.orig/kernel/time/timekeeping.c 2008-01-16 12:21:46.000000000 -0800 > > > +++ monotonic-cleanup/kernel/time/timekeeping.c 2008-01-16 14:15:31.000000000 -0800 > > > @@ -71,10 +71,12 @@ > > > */ > > > static inline s64 __get_nsec_offset(void) > > > { > > > - cycle_t cycle_delta; > > > + cycle_t now, cycle_delta; > > > s64 ns_offset; > > > > > > - cycle_delta = clocksource_get_cycles(clock, clocksource_read(clock)); > > > + now = clocksource_read(clock); > > > + cycle_delta = (now - clock->cycle_last) & clock->mask; > > > + cycle_delta += clock->cycle_accumulated; > > > > Is the above just to decouple the two methods? > > Yep. clocksource_get_cycles() ended up not being as useful as an helper > function (I was hoping the arch vsyscall implementations could use it, > but they've done too much optimization - although that may reflect a > need up the chain to the clocksource structure). > The problem with vsyscall is that we will have a hard time disabling preemption :( Therefore, insuring that the read of the data is done in a timely manner is hard to do. Mathieu > thanks > -john > > -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- 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/