Re: 2.6.27.5 guest boot failure using in-kernel PIT

[Jan Kiszka <jan.kiszka@web.de>]

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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...

Jan


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