On (Fri) 29 Aug 2014 [15:45:30], Zhang Haoyu wrote: > Hi, all > > I start a VM with virtio-serial (default ports number: 31), and found that virtio-blk performance degradation happened, about 25%, this problem can be reproduced 100%. > without virtio-serial: > 4k-read-random 1186 IOPS > with virtio-serial: > 4k-read-random 871 IOPS > > but if use max_ports=2 option to limit the max number of virio-serial ports, then the IO performance degradation is not so serious, about 5%. > > And, ide performance degradation does not happen with virtio-serial. Pretty sure it's related to MSI vectors in use. It's possible that the virtio-serial device takes up all the avl vectors in the guests, leaving old-style irqs for the virtio-blk device. If you restrict the number of vectors the virtio-serial device gets (using the -device virtio-serial-pci,vectors= param), does that make things better for you? Amit -- 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
