From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754424AbcITXIm (ORCPT ); Tue, 20 Sep 2016 19:08:42 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35999 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753204AbcITXIj (ORCPT ); Tue, 20 Sep 2016 19:08:39 -0400 From: Nicolai Stange To: Thomas Gleixner Cc: Nicolai Stange , John Stultz , linux-kernel@vger.kernel.org Subject: Re: [RFC v7 00/23] adapt clockevents frequencies to mono clock References: <20160916200851.9273-1-nicstange@gmail.com> Date: Wed, 21 Sep 2016 01:08:36 +0200 In-Reply-To: (Thomas Gleixner's message of "Tue, 20 Sep 2016 22:54:02 +0200 (CEST)") Message-ID: <877fa641aj.fsf@gmail.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (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 Fri, 16 Sep 2016, Nicolai Stange wrote: > >> Goal: avoid programming ced devices too early for large deltas, for >> details, c.f. the description of [21/23]. >> >> [21-23/23] Actually do the frequency adjustments. >> >> Tested on x86_64 and next-20160916. > > Have you ever measured the overhead of the extra work which has to be done > in clockevents_adjust_all_freqs() ? Not exactly, I had a look at its invocation frequency which seems to decay exponentially with uptime, presumably because the NTP error approaches zero. However, I've just gathered a function_graph ftrace on my Intel i7-4800MQ (Haswell, 8HTs): # tracer: function_graph # # TIME CPU DURATION FUNCTION CALLS # | | | | | | | | 85.287027 | 0) 0.899 us | clockevents_adjust_all_freqs(); 85.288026 | 0) 0.759 us | clockevents_adjust_all_freqs(); 85.289026 | 0) 0.735 us | clockevents_adjust_all_freqs(); 85.290026 | 0) 0.671 us | clockevents_adjust_all_freqs(); 149.503656 | 2) 2.477 us | clockevents_adjust_all_freqs(); 149.507660 | 2) 2.308 us | clockevents_adjust_all_freqs(); 149.511658 | 2) 2.651 us | clockevents_adjust_all_freqs(); 149.545660 | 0) 2.268 us | clockevents_adjust_all_freqs(); 149.564211 | 2) 2.321 us | clockevents_adjust_all_freqs(); 214.351899 | 2) 1.520 us | clockevents_adjust_all_freqs(); 214.354935 | 0) 1.053 us | clockevents_adjust_all_freqs(); 279.026205 | 0) 2.289 us | clockevents_adjust_all_freqs(); 279.030195 | 0) 2.190 us | clockevents_adjust_all_freqs(); 279.034196 | 0) 2.381 us | clockevents_adjust_all_freqs(); 279.047492 | 2) 2.390 us | clockevents_adjust_all_freqs(); 344.250356 | 1) 2.727 us | clockevents_adjust_all_freqs(); 408.879538 | 1) 2.235 us | clockevents_adjust_all_freqs(); 473.125730 | 6) 1.513 us | clockevents_adjust_all_freqs(); 473.129731 | 6) 1.650 us | clockevents_adjust_all_freqs(); 538.387891 | 3) 2.305 us | clockevents_adjust_all_freqs(); 538.391890 | 3) 2.300 us | clockevents_adjust_all_freqs(); 668.257162 | 3) 2.691 us | clockevents_adjust_all_freqs(); 668.261162 | 3) 2.306 us | clockevents_adjust_all_freqs(); 733.459261 | 0) 1.066 us | clockevents_adjust_all_freqs(); 733.463261 | 0) 1.233 us | clockevents_adjust_all_freqs(); 733.467263 | 1) 1.382 us | clockevents_adjust_all_freqs(); 863.398561 | 2) 2.218 us | clockevents_adjust_all_freqs(); 863.402552 | 2) 2.792 us | clockevents_adjust_all_freqs(); 1122.210001 | 3) 2.259 us | clockevents_adjust_all_freqs(); 1122.214004 | 3) 2.165 us | clockevents_adjust_all_freqs(); 1381.283287 | 2) 1.944 us | clockevents_adjust_all_freqs(); 1895.664008 | 2) 1.940 us | clockevents_adjust_all_freqs(); 1895.668009 | 2) 2.041 us | clockevents_adjust_all_freqs(); 2930.385388 | 0) 1.067 us | clockevents_adjust_all_freqs(); 2930.386390 | 5) 1.208 us | clockevents_adjust_all_freqs(); Thanks, Nicolai