From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753661AbbJTIyS (ORCPT ); Tue, 20 Oct 2015 04:54:18 -0400 Received: from mail-wi0-f177.google.com ([209.85.212.177]:36966 "EHLO mail-wi0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752386AbbJTIyN (ORCPT ); Tue, 20 Oct 2015 04:54:13 -0400 Date: Tue, 20 Oct 2015 10:54:08 +0200 From: Richard Cochran To: John Stultz Cc: Christopher Hall , Thomas Gleixner , Jeff Kirsher , "H. Peter Anvin" , Ingo Molnar , Peter Zijlstra , "x86@kernel.org" , intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, lkml , kevin.b.stanton@intel.com Subject: Re: [PATCH v4 1/4] Produce system time from correlated clocksource Message-ID: <20151020085408.GA2542@netboy> References: <1444675522-4198-1-git-send-email-christopher.s.hall@intel.com> <1444675522-4198-2-git-send-email-christopher.s.hall@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 19, 2015 at 05:36:56PM -0700, John Stultz wrote: > If we're only tracking 4ms of history, how does this solution > measurably improve the error over using the timestamps to generate > MONOTONIC_RAW clock deltas (which doesn't require keeping any history) > and using getnstime_raw_and_real to take an anchor point to calculate > the delta from? Why is adding complexity necessary? This idea is variant of what I suggested in another reply in this thread. To my understanding, there is no need at all to keep a history arbitrarily 4 ms long. Instead, the DSP driver (or whoever else may need such a thing) can simply sample the system time at the rate needed for that particular application. Thanks, Richard