On Fri, Feb 22, 2008 at 08:45:00PM +0200, Avi Kivity wrote: > Marcelo Tosatti wrote: > >Another source of problems in this area is that the TSC_OFFSET is > >initialized to represent zero at different times for VCPU0 (at boot) and > >the remaining ones (at APIC_DM_INIT). > > > > > > I added tsc sync in the guest bios some time ago, so this should be > solved now. > > >>This will improve tsc quality for those machines, but we can't depend on > >>it, since some machines don't have constant tsc. Further, I don't think > >>really large machines can have constant tsc since clock distribution > >>becomes difficult or impossible. > >> > > > >As discussed earlier, in case the host kernel does not have the TSC > >stable, it needs to enforce a state which the guest OS will not trust > >the TSC. The easier way to do that is to fake a C3 state. However, QEMU > >does not emulate IO port based wait. This appears to be the reason for > >the high-CPU-usage-on-idle with Windows guests, fixed by disabling C3 > >reporting on rombios (commit cb98751267c2d79f5674301ccac6c6b5c2e0c6b5 of > >kvm-userspace). > > > > > > Oh. Can you point me at documentation for the io port wait thing?
ACPI spec 3.0b section 4.7.3.5. Reading LVL2 or LVL3 register will cause the processor to enter the specified C state. See drivers/acpi/processor_idle.c::acpi_idle_do_entry. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
