On Mon, Jun 29, 2009 at 12:22:35PM +0200, Ingo Molnar wrote: > > * Gleb Natapov <gleb@xxxxxxxxxx> wrote: > > > KVM would like to provide x2APIC interface to a guest without emulating > > interrupt remapping device. The reason KVM prefers guest to use x2APIC > > is that x2APIC interface is better virtualizable and provides better > > performance than mmio xAPIC interface: > > > > - msr exits are faster than mmio (no page table walk, emulation) > > - no need to read back ICR to look at the busy bit > > - one 64 bit ICR write instead of two 32 bit writes > > - shared code with the Hyper-V paravirt interface > > > > Included patch changes x2APIC enabling logic to enable it even if IR > > initialization failed, but kernel runs under KVM and no apic id is > > greater than 255 (if there is one spec requires BIOS to move to x2apic > > mode before starting an OS). > > > > Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx> > > --- > > > > v2: > > Add help message to Kconfig > > Force physical mode if IR is not available. > > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index d1430ef..3e5b6ea 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -260,12 +260,15 @@ config SMP > > > > config X86_X2APIC > > bool "Support x2apic" > > - depends on X86_LOCAL_APIC && X86_64 && INTR_REMAP > > + depends on X86_LOCAL_APIC && X86_64 > > Have you tried to build this with X86_X2APIC set but INTR_REMAP > disabled? > Yes. I notice that X86_X2APIC depends on INTR_REMAP when I did it. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
