From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751454AbcGMNJI (ORCPT ); Wed, 13 Jul 2016 09:09:08 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:33235 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750883AbcGMNJC (ORCPT ); Wed, 13 Jul 2016 09:09:02 -0400 From: Nicolai Stange To: Thomas Gleixner Cc: Nicolai Stange , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, John Stultz , Borislav Petkov , Paolo Bonzini , Viresh Kumar , Hidehiro Kawai , "Peter Zijlstra \(Intel\)" , "Christopher S. Hall" , Adrian Hunter , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/4] kernel/time/clockevents: compensate for monotonic clock's dynamic frequency References: <20160710193047.18320-1-nicstange@gmail.com> <20160710193047.18320-5-nicstange@gmail.com> <87inwcd6s7.fsf@gmail.com> <87poqjm7r2.fsf@gmail.com> Date: Wed, 13 Jul 2016 15:08:33 +0200 In-Reply-To: (Thomas Gleixner's message of "Tue, 12 Jul 2016 17:04:17 +0200 (CEST)") Message-ID: <871t2xy9bi.fsf@gmail.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.94 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thomas Gleixner writes: > On Tue, 12 Jul 2016, Nicolai Stange wrote: >> Another issue is that ->min_delta_ns and ->max_delta_ns are measured in >> raw clock time while the delta in clockevents_program_event() would now >> be interpreted as being in monotonic clock time: >> clc = ((unsigned long long) delta * dev->mult_mono) >> dev->shift; > > Does that really matter much? > >> Ideally, I'd like to get rid of ->min_delta_ns and ->max_delta_ns >> alltogether and consistently use the ->min_delta_ticks and >> ->max_delta_ticks instead. AFAICS, ->min_delta_ns is really needed only >> for setting dev->next_event in clockevents_program_min_delta(). >> dev->next_event is read only from __clockevents_update_freq() for >> reprogramming purposes and thus, assuming 0 for ->delta_min_ns in >> clockevents_program_min_delta() would probably work: a reprogramming >> would invoke clockevents_program_min_delta() once again. > > I completely fail to parse the above paragraph. > >> The downside of this approach is that a quick grep reveals 40 clockevent >> device drivers whose initialization code would need to get touched in >> order to convert them from min_delta_ns/max_delta_ns to >> min_delta_ticks/max_delta_ticks. >> >> So, the question is whether I should do all of this or whether the >> doubled timer interrupts aren't annoying enough to justify such a big >> change? > > Can you provide an initial patch which does the adjustment w/o all the related > churn so we can see how intrusive that gets? Please see the RFC tagged series at http://lkml.kernel.org/g/20160713130017.8202-1-nicstange@gmail.com I tried to answer/address your above questions in the cover letter. Note that I split the x86 TSC related patches off: http://lkml.kernel.org/g/20160713130344.8319-1-nicstange@gmail.com Thanks, Nicolai