Re: [RFC 00/20] ns: Introduce Time Namespace

[Thomas Gleixner]

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