Re: [Qemu-devel] TSC in qem[-kvm] 1.1+ and in-kernel irqchip

[Gleb Natapov <gleb@redhat.com>]

On Fri, Aug 10, 2012 at 01:24:06PM +0400, Michael Tokarev wrote:
> On 10.08.2012 11:33, Gleb Natapov wrote:
> > On Thu, Aug 09, 2012 at 10:27:43PM +0400, Michael Tokarev wrote:
> >> As a follow-up to the patch "tsc: use kvmclock for
> >> calibration".
> >>
> >> There's another problem reported by several users.
> >> The sympthom is that grub does not show boot menu,
> >> it boots default entry right away without any pause.
> >>
> >> After quite some debugging it turned out to be
> >> TSC issue.  Grub uses tsc for its timeout handling.
> >> When setting timeout to some very large value
> >> (10000), I can see the counter is ticking backwards
> >> at a very high speed, ticking from 10000 to 0 in
> >> about 5 seconds.
> >>
> >> Running kvm -cpu host,-tsc forces grub to use
> >> rtc clocksource, and the problem goes away.
> >>
> > Can you try -no-kvm-pit-reinjection please.
> 
> It does not help.  With -no-kvm-pit-reinjection, the
> time in grub is ticking about 1000 times faster still,
> just like without.
> 
> >> The most interesting thing is that this is a
> >> problem new for qemu-kvm 1.1 (and is still
> >> present in current git), 1.0 version had no
> >> such issue.  And it only happens when in-kernel
> >> irqchip is enabled -- running with -no-kvm-irqchip
> >> also fixes the grub problem, so that tsc starts
> >> counting "correctly" for grub again.
> >>
> > 1.0 work on the same kernel 1.1 doesn't?
> 
> Yes.  This issue does not look like kernel-dependent -
> it happens the same way on 3.0, 3.2 and 3.5 kernels.
> Note that upstream qemu 1.1+ is also affected, when
> used with -machine pc,kernel_irqchip=on.
> 
Any chance to bisect it?

--
			Gleb.