Eduardo Habkost wrote: > 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?
Yeah, they are, so you won't benefit from them for in-kernel cases. But with in-kernel emulation just the probability of coalesced ticks is a bit lower, they cannot be avoided either. > I am seeing the problem here > when using the in-kernel PIT, but (surprisingly) my setup works when > using -no-kvm-pit. Weird, makes no sense to me as well ATM. Jan
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