Re: 2.6.27.5 guest boot failure using in-kernel PIT

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Nov 21, 2008 at 08:54:56AM +0100, Jan Kiszka wrote:
> Eduardo Habkost wrote:
> > On Thu, Nov 20, 2008 at 12:22:53PM -0200, Eduardo Habkost wrote:
> >> Hi,
> >>
> >> When using a kvm.git kernel as host, I am getting guest boot failures
> >> when booting Fedora Rawhide kernel (2.6.27.5-117.fc10.x86_64). Guest
> >> stops booting at:
> >>
> >> ENABLING IO-APIC IRQs
> >> ..TIMER: vector=0x30 apic1=0 pin1=0 apic2=-1 pin2=-1
> >> ..MP-BIOS bug: 8254 timer not connected to IO-APIC
> >> ...trying to set up timer (IRQ0) through the 8259A ...
> >> ..... (found apic 0 pin 0) ...
> >> ....... failed.
> >> ...trying to set up timer as Virtual Wire IRQ...
> >> ..... failed.
> >> ...trying to set up timer as ExtINT IRQ...
> > 
> > I've just found out this problem happens because the guest has HZ=1000
> > and the host had HZ=250 and no CONFIG_HIGH_RES_TIMERS.
> > 
> > With this setup, the host is not managing to inject enough timer
> > interrupts during the mdelay() loop on timer_irq_works().
> > 
> 
> Interesting, and plausible.
> 
> My observation so far is a sporadic test failure, often correlating with
> some raised host OS load. I'm running a high-res kernel, but that cannot
> prevent that this only 10 ticks long loop of the guest may obtain too
> few CPU cycles to handle enough of them once in a while (IIRC, it needs
> 4 out of the 10 ticks to declare the timer routing functional).
> 
> Maybe Gleb's anti-coalesce patches for the PIC can also deal with your
> timer resolution conflict. At least worth a try...

Aren't Gleb patches for the userspace PIT? I am seeing the problem here
when using the in-kernel PIT, but (surprisingly) my setup works when
using -no-kvm-pit.

-- 
Eduardo