On Fri, Nov 21, 2008 at 3:10 PM, Marcelo Tosatti <[EMAIL PROTECTED]> wrote:
> Hi Jan,
>
> 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).
>
> Using in-kernel PIT?
>
> This is a potential problem which can be worked around by disabling the
> whole thing either via no_timer_check or paravirt equivalent (Glauber?)
> but for the non-paravirt case it seems its not the culprit. Possible
> failure scenarios:
For KVM_CLOCK case, I believe there's absolutely no reason to be more
complicated than than that:
+extern int no_timer_check;
+
void __init kvmclock_init(void)
{
if (!kvm_para_available())
@@ -178,6 +180,8 @@ void __init kvmclock_init(void)
if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
if (kvm_register_clock("boot clock"))
return;
+
+ no_timer_check = 1;
pv_time_ops.get_wallclock = kvm_get_wallclock;
pv_time_ops.set_wallclock = kvm_set_wallclock;
pv_time_ops.sched_clock = kvm_clock_read;
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