From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH v4 1/4] Produce system time from correlated clocksource Date: Tue, 20 Oct 2015 12:48:03 +0200 (CEST) Message-ID: References: <1444675522-4198-1-git-send-email-christopher.s.hall@intel.com> <1444675522-4198-2-git-send-email-christopher.s.hall@intel.com> <20151020085408.GA2542@netboy> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: John Stultz , Christopher Hall , 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 To: Richard Cochran Return-path: In-Reply-To: <20151020085408.GA2542@netboy> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, 20 Oct 2015, Richard Cochran wrote: > 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. That's complete nonsense. The whole point is to have a proper correlation from ART/audio timestamps to system time. Sampling system time does not help in any way, Thanks, tglx