Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752881AbdHBRKR (ORCPT ); Wed, 2 Aug 2017 13:10:17 -0400 Received: from mail-qt0-f169.google.com ([209.85.216.169]:37950 "EHLO mail-qt0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752035AbdHBRIz (ORCPT ); Wed, 2 Aug 2017 13:08:55 -0400 MIME-Version: 1.0 In-Reply-To: <1501684690-211093-2-git-send-email-dplotnikov@virtuozzo.com> References: <1501684690-211093-1-git-send-email-dplotnikov@virtuozzo.com> <1501684690-211093-2-git-send-email-dplotnikov@virtuozzo.com> From: John Stultz Date: Wed, 2 Aug 2017 10:08:54 -0700 Message-ID: Subject: Re: [PATCH v4 01/10] timekeeper: introduce extended clocksource reading callback To: Denis Plotnikov Cc: Paolo Bonzini , Radim Krcmar , kvm list , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , lkml , "x86@kernel.org" , rkagan@virtuozzo.com, den@virtuozzo.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2436 Lines: 55 On Wed, Aug 2, 2017 at 7:38 AM, Denis Plotnikov wrote: > The callback provides extended information about just read > clocksource value. > > It's going to be used in cases when detailed system information > needed for further time related values calculation, e.g in KVM > masterclock settings calculation. > > Signed-off-by: Denis Plotnikov > --- > include/linux/clocksource.h | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h > index a78cb18..786a522 100644 > --- a/include/linux/clocksource.h > +++ b/include/linux/clocksource.h > @@ -48,7 +48,14 @@ struct module; > * 400-499: Perfect > * The ideal clocksource. A must-use where > * available. > - * @read: returns a cycle value, passes clocksource as argument > + * @read: returns a cycle value (might be not quite cycles: > + * see pvclock) passes clocksource as argument > + * @read_with_stamp: saves cycles value (got from timekeeper) and cycles > + * stamp (got from hardware counter value and used by > + * timekeeper to calculate the cycles value) to > + * corresponding input pointers return true if cycles > + * stamp holds real cycles and false if it holds some > + * time derivative value > * @enable: optional function to enable the clocksource > * @disable: optional function to disable the clocksource > * @mask: bitmask for two's complement > @@ -78,6 +85,8 @@ struct module; > */ > struct clocksource { > u64 (*read)(struct clocksource *cs); > + bool (*read_with_stamp)(struct clocksource *cs, > + u64 *cycles, u64 *cycles_stamp); > u64 mask; I'm not really fan of an interface that leaks magic data to users that know enough. And its not clear from this if the magic data is standardized or different clocksources export different data? What exactly are the attributes you're trying to pull from the lower-level hardware that you can't get otherwise (without using the update_pvclock_gtod() since, if I'm understanding that apparently gives you too much detail to deal with)? thanks -john