Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751614AbZGaINF (ORCPT ); Fri, 31 Jul 2009 04:13:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751302AbZGaINE (ORCPT ); Fri, 31 Jul 2009 04:13:04 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:57994 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751095AbZGaINC (ORCPT ); Fri, 31 Jul 2009 04:13:02 -0400 Subject: Re: [RFC][patch 10/12] move NTP adjusted clock multiplier to struct timekeeper From: john stultz To: Martin Schwidefsky Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner , Daniel Walker In-Reply-To: <20090731095254.3ed0cb7d@skybase> References: <20090729134125.313191633@de.ibm.com> <20090729134231.515027738@de.ibm.com> <1248991488.3374.14.camel@localhost> <20090731095254.3ed0cb7d@skybase> Content-Type: text/plain Date: Fri, 31 Jul 2009 01:12:59 -0700 Message-Id: <1249027979.3333.8.camel@work-vm> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4007 Lines: 87 On Fri, 2009-07-31 at 09:52 +0200, Martin Schwidefsky wrote: > On Thu, 30 Jul 2009 15:04:48 -0700 > john stultz wrote: > > > On Wed, 2009-07-29 at 15:41 +0200, Martin Schwidefsky wrote: > > > plain text document attachment (timekeeper-mult.diff) > > > From: Martin Schwidefsky > > > > > > The clocksource structure has two multipliers, the unmodified multiplier > > > clock->mult_orig and the NTP corrected multiplier clock->mult. The NTP > > > multiplier is misplaced in the struct clocksource, this is private > > > information of the timekeeping code. Add the mult field to the struct > > > timekeeper to contain the NTP corrected value, keep the unmodifed > > > multiplier in clock->mult and remove clock->mult_orig. For consistency > > > add the shift value associated with the NTP corrected mult value to > > > struct timekeeper as well. > > > > > > Cc: Ingo Molnar > > > Cc: Thomas Gleixner > > > Cc: john stultz > > > Cc: Daniel Walker > > > Signed-off-by: Martin Schwidefsky > > > --- > > > arch/arm/plat-omap/common.c | 2 +- > > > include/linux/clocksource.h | 4 +--- > > > kernel/time/timekeeping.c | 43 +++++++++++++++++++++++++------------------ > > > 3 files changed, 27 insertions(+), 22 deletions(-) > > > > > > Index: linux-2.6/include/linux/clocksource.h > > > =================================================================== > > > --- linux-2.6.orig/include/linux/clocksource.h > > > +++ linux-2.6/include/linux/clocksource.h > > > @@ -149,8 +149,7 @@ extern u64 timecounter_cyc2time(struct t > > > * @disable: optional function to disable the clocksource > > > * @mask: bitmask for two's complement > > > * subtraction of non 64 bit counters > > > - * @mult: cycle to nanosecond multiplier (adjusted by NTP) > > > - * @mult_orig: cycle to nanosecond multiplier (unadjusted by NTP) > > > + * @mult: cycle to nanosecond multiplier > > > * @shift: cycle to nanosecond divisor (power of two) > > > * @flags: flags describing special properties > > > * @vread: vsyscall based read > > > @@ -168,7 +167,6 @@ struct clocksource { > > > void (*disable)(struct clocksource *cs); > > > cycle_t mask; > > > u32 mult; > > > - u32 mult_orig; > > > u32 shift; > > > unsigned long flags; > > > cycle_t (*vread)(void); > > > Index: linux-2.6/kernel/time/timekeeping.c > > > =================================================================== > > > --- linux-2.6.orig/kernel/time/timekeeping.c > > > +++ linux-2.6/kernel/time/timekeeping.c > > > @@ -29,6 +29,8 @@ struct timekeeper { > > > s64 ntp_error; > > > int xtime_shift; > > > int ntp_error_shift; > > > + u32 mult; /* NTP adjusted clock multiplier */ > > > + u32 shift; /* NTP adjusted clock shift */ > > > > I'm a little confused here. NTP doesn't adjust the shift value. This > > seems redundant with the xtime_shift value introduced in [patch 9/12]. > > True the NTP code does not adjust the shift value. But mult and shift > build a pair, no? I think it is more readable if we use timekeeper.mult > and timekeeper.shift instead of timekeeper.mult and clock->shift. > And the xtime_shift does not need to be the same value as the clock > shift - at least in theory. It is just a shift to increase precision. > Therefore I would like to use the xtime_shift and ntp_error_shift values > exclusively as the shifts for the respective xtime_nsec and ntp_error > values. Makes sense ? But can't we drop the xtime_shift if we have the clocksource shift kept internally? Unless I'm missing something more subtle in your patches, they should be the same at all times. 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/