The PIIX4 ACPI controller prior to revision 0x3 contains a bug where reading of the timer port is unreliable, so the kernel reads it three times for consistency check.
QEMU does not suffer from that problem :) The datasheet for PIIX4, PIIX4E, and PIIX4M is the same. I failed to find any indication that the revision increase could affect anything other than the PMTimer port read. This reduces idle guest CPU consumption from 14% to 8% on 4-way KVM guest. --- kvm-userspace.orig/qemu/hw/acpi.c +++ kvm-userspace/qemu/hw/acpi.c @@ -486,7 +486,7 @@ i2c_bus *piix4_pm_init(PCIBus *bus, int pci_conf[0x03] = 0x71; pci_conf[0x06] = 0x80; pci_conf[0x07] = 0x02; - pci_conf[0x08] = 0x00; // revision number + pci_conf[0x08] = 0x03; // revision number pci_conf[0x09] = 0x00; pci_conf[0x0a] = 0x80; // other bridge device pci_conf[0x0b] = 0x06; // bridge device ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel