From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [RFC 00/20] ns: Introduce Time Namespace Date: Tue, 2 Oct 2018 08:15:15 +0200 (CEST) Message-ID: References: <20180919205037.9574-1-dima@arista.com> <874lej6nny.fsf@xmission.com> <20180924205119.GA14833@outlook.office365.com> <874leezh8n.fsf@xmission.com> <20180925014150.GA6302@outlook.office365.com> <87zhw4rwiq.fsf@xmission.com> <20181001232033.GA31324@outlook.office365.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <20181001232033.GA31324@outlook.office365.com> Sender: linux-kernel-owner@vger.kernel.org To: Andrey Vagin Cc: "Eric W. Biederman" , Dmitry Safonov , "linux-kernel@vger.kernel.org" , Dmitry Safonov <0x7f454c46@gmail.com>, Adrian Reber , Andy Lutomirski , Christian Brauner , Cyrill Gorcunov , "H. Peter Anvin" , Ingo Molnar , Jeff Dike , Oleg Nesterov , Pavel Emelianov , Shuah Khan , "containers@lists.linux-foundation.org" , "criu@openvz.org" , "linux-api@vger.kernel.org" , "x86@kernel.org" , Alexey List-Id: linux-api@vger.kernel.org On Mon, 1 Oct 2018, Andrey Vagin wrote: > On Thu, Sep 27, 2018 at 11:41:49PM +0200, Thomas Gleixner wrote: > > On Thu, 27 Sep 2018, Thomas Gleixner wrote: > > > Add time skew via NTP/PTP into the picture and you might have to adjust > > > timers as well, because you need to guarantee that they are not expiring > > > early. > > > > > > I haven't looked through Dimitry's patches yet, but I don't see how this > > > can work at all without introducing subtle issues all over the place. > > > > And just a quick scan tells me that this is broken. Timers will expire > > early or late. The latter is acceptible to some extent, but larger delays > > might come with surprise. Expiring early is an absolute nono. > > Do you mean that we have to adjust all timers after changing offset for > CLOCK_MONOTONIC or CLOCK_BOOTTIME? Our idea is that offsets for > monotonic and boot times will be set immediately after creating a time > namespace before using any timers. I explained that in detail in this thread, but it's not about the initial setting of clock mono/boot before any timers have been armed. It's about setting the offset or clock realtime (via settimeofday) when timers are already armed. Also having a entirely different time domain, e.g. separate NTP adjustments, makes that necessary. Thanks, tglx