Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754530AbYAQC2b (ORCPT ); Wed, 16 Jan 2008 21:28:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752114AbYAQC2U (ORCPT ); Wed, 16 Jan 2008 21:28:20 -0500 Received: from e5.ny.us.ibm.com ([32.97.182.145]:58507 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751353AbYAQC2T (ORCPT ); Wed, 16 Jan 2008 21:28:19 -0500 Subject: Re: [RFC PATCH 16/22 -v2] add get_monotonic_cycles From: john stultz To: Steven Rostedt Cc: Mathieu Desnoyers , 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 In-Reply-To: References: <20080109232914.676624725@goodmis.org> <20080109233044.777564395@goodmis.org> <20080115214636.GD17439@Krystal> <20080115220824.GB22242@Krystal> <20080116031730.GA2164@Krystal> <20080116145604.GB31329@Krystal> <1f1b08da0801161436k4a7ac1e3kd83590951e7bebb9@mail.gmail.com> <1200523867.6127.5.camel@localhost.localdomain> Content-Type: text/plain Date: Wed, 16 Jan 2008 18:28:09 -0800 Message-Id: <1200536889.6127.52.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.12.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1877 Lines: 53 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). 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/