Re: [PATCH 0/4] paravirt clock patches

Marcelo Tosatti
2008-05-05T15:32:58Z

On Mon, May 05, 2008 at 09:47:59AM +0200, Gerd Hoffmann wrote:
> Marcelo Tosatti wrote:
> > On Thu, Apr 24, 2008 at 10:37:04AM +0200, Gerd Hoffmann wrote:
> >> Hi folks,
> >>
> >> My first attempt to send out a patch series with git ...
> >>
> >> The patches fix the kvm paravirt clocksource code to be compatible with
> >> xen and they also factor out some code which can be shared into a
> >> separate source files used by both kvm and xen.
> >
> > The issue with SMP guests is still present. Booting with "nohz=off" resolves it.
> >
> > Same symptoms as before, apic_timer_fn for one of the vcpu's is ticking way slower
> > than the remaining ones:
> >
> > [root@localhost ~]# cat /proc/timer_stats | grep apic
> > 391, 4125 qemu-system-x86 apic_mmio_write (apic_timer_fn)
> > 2103, 4126 qemu-system-x86 apic_mmio_write (apic_timer_fn)
> > 1896, 4127 qemu-system-x86 apic_mmio_write (apic_timer_fn)
> > 1857, 4128 qemu-system-x86 apic_mmio_write (apic_timer_fn)
>
> What userspace version is this? With iothread support? Or older one
> where the vcpu0 thread also handles all the I/O? Is 4x neeed to
> reproduce or do you see it with 2x too? What host?

F8 host, recent kvm-userspace.git (so with IO thread), recent kvm.git
(plus your patches), haven't tried 2x but I think 4x is not necessary to
reproduce the problem.

> A quick test with xenner (which has a separate I/O thread) didn't show
> anything unusual. Going investigate ...

Give a pure kvm guest a try, its pretty easy to reproduce.