Saul Tamari wrote:
Hi, There seems to be a bug in the VirtIO guest device driver (tested with 2.6.31.5 kernel). The bug causes frequent & excessive VIRTIO_PCI_ISR reads (causing PIO vm-exits) for a device that is not being used. The setup I’m using includes two VirtIO block devices – vda & vdb. While running heavy IO on vdb I notice a lot of VIRTIO_PCI_ISR port reads for the PIO ports of vda too. For each vdb IO operation passed to the hypervisor by the virtio driver I see: 1. One VIRTIO_PCI_QUEUE_NOTIFY write on vdb 2. One VIRTIO_PCI_ISR read on vdb 3. One VIRTIO_PCI_ISR read on vda (while not explicitly using vda)
That's because it's using a shared interrupt and each device needs to check whether it's got pending work to do.
You can eliminate this by using MSI-x. Regards, Anthony Liguori -- 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
