From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: [RFC v3 net-next 13/18] net/sched: Introduce the TBS Qdisc Date: Thu, 12 Apr 2018 08:03:49 -0700 Message-ID: <20180412150349.3dgkgqx4ged6t4ng@localhost> References: <2897b562-06e0-0fcc-4fb1-e8c4469c0faa@intel.com> <60799930-56a0-3692-9482-e733d7277152@intel.com> <0369f48c-b48e-ce27-1988-8bc0ec65bf13@intel.com> <3d1c27a2-7a21-ab80-e92b-47b415b70548@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Thomas Gleixner , netdev@vger.kernel.org, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, vinicius.gomes@intel.com, anna-maria@linutronix.de, henrik@austad.us, John Stultz , levi.pearson@harman.com, edumazet@google.com, willemb@google.com, mlichvar@redhat.com To: Jesus Sanchez-Palencia Return-path: Received: from mail-pf0-f196.google.com ([209.85.192.196]:36420 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753219AbeDLPDx (ORCPT ); Thu, 12 Apr 2018 11:03:53 -0400 Received: by mail-pf0-f196.google.com with SMTP id g14so3946255pfh.3 for ; Thu, 12 Apr 2018 08:03:53 -0700 (PDT) Content-Disposition: inline In-Reply-To: <3d1c27a2-7a21-ab80-e92b-47b415b70548@intel.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Apr 11, 2018 at 04:38:44PM -0700, Jesus Sanchez-Palencia wrote: > Just breaking this down a bit, yes, TAI is the network time base, and the NICs > PTP clock use that because PTP is (commonly) based on TAI. After the PHCs have > been synchronized over the network (e.g. with ptp4l), my understanding is that > if applications want to use the clockid_t CLOCK_TAI as a network clock reference > it's required that something (i.e. phc2sys) is synchronizing the PHCs and the > system clock, and also that something calls adjtime to apply the TAI vs UTC > offset to CLOCK_TAI. Yes. I haven't seen any distro that sets the TAI-UTC offset after boot, nor are there any user space tools for this. The kernel is ready, though. > I was thinking about the full offload use-cases, thus when no scheduling is > happening inside the qdiscs. Applications could just read the time from the PHC > clocks directly without having to rely on any of the above. On this case, > userspace would use DYNAMIC_CLOCK just to flag that this is the case, but I must > admit it's not clear to me how common of a use-case that is, or even if it makes > sense. 1588 allows only two timescales, TAI and ARB-itrary. Although it doesn't make too much sense to use ARB, still people will do strange things. Probably some people use UTC. I am not advocating supporting alternate timescales, just pointing out the possibility. Thanks, Richard