Re: [kvm-devel] [PATCH 0/4] paravirt clock patches

[Marcelo T. <mto...@re...>]

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.