From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933024AbbIDO2k (ORCPT ); Fri, 4 Sep 2015 10:28:40 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:52528 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753532AbbIDO2i (ORCPT ); Fri, 4 Sep 2015 10:28:38 -0400 Date: Fri, 4 Sep 2015 16:28:27 +0200 From: Peter Zijlstra To: Richard Cochran Cc: "Hall, Christopher S" , Thomas Gleixner , "Kirsher, Jeffrey T" , "hpa@zytor.com" , "mingo@redhat.com" , "john.stultz@linaro.org" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "intel-wired-lan@lists.osuosl.org" Subject: Re: [PATCH v3 1/4] Add correlated clocksource deriving system time from an auxiliary clocksource Message-ID: <20150904142827.GE18489@twins.programming.kicks-ass.net> References: <1440183128-1384-1-git-send-email-christopher.s.hall@intel.com> <1440183128-1384-2-git-send-email-christopher.s.hall@intel.com> <20150904081122.GA4201@netboy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150904081122.GA4201@netboy> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 04, 2015 at 10:11:22AM +0200, Richard Cochran wrote: > On Thu, Sep 03, 2015 at 11:20:37PM +0000, Hall, Christopher S wrote: > > In addition to the network interface, ART will be used in the audio interface as well. > > We need to support the case where an audio co-processor will control the audio device. > > In this case, the get_ts() function supplied by the audio driver will be very slow > > (several milliseconds) and the result will be out of date by some fraction of that > > amount. > > Why does it take milliseconds to read one audio time stamp? So what I suspect, but please correct me if I'm wrong Chris, is that a DSP will buffer and process audio signals, and only later wake up the main CPU. So by the time the CPU is made aware of the data, it's 'old'.