Re: netbsd PVH dom0: xen clock event stops

[Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>]

On Sun, Nov 15, 2020 at 07:24:16PM +0100, Roger Pau Monné wrote:
> On Sun, Nov 15, 2020 at 06:49:38PM +0100, Manuel Bouyer wrote:
> > Hello,
> > I spent some more time debugging NetBSD as a PVH dom0 on Xen,
> > With Roger's patch to avoid a Xen panic, the NetBSD kernel stalls
> > configuring devices. At first I though it was an issue with hardware
> > interrupts, but it more likely is an issue with Xen timer events.
> > Specifically: virtual CPU 0 stops receiving timer events, while other
> > CPUs keep receiving them. I tried to force a timer rearm but this didn't 
> > help.
> > The event is not masked nor pending on Xen or NetBSD, as confirmed by 'q'.
> > Others events (the Xen console, the debug event) are properly received
> > by CPU0. I don't know how to debug this more at this point.
> 
> You could try to use dom0_vcpus_pin command line option and then dump
> the timers using the 'a' debug key, this way you can see if CPU0 has a
> timer pending (which would be the vCPU0 timer).
> 
> What timer is NetBSD using, is it the PV vCPU single shot timer, the
> periodic one, or the emulated local APIC timer?

It is the PV single shot timer, I guess. But used as a periodic
timer by rearming it in the handler:
        next = ci->ci_xen_hardclock_systime_ns + NS_PER_TICK;
        error = HYPERVISOR_set_timer_op(next);

-- 
Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
     NetBSD: 26 ans d'experience feront toujours la difference
--