>>>>>> If virtio-blk and virtio-serial share an IRQ, the guest operating system has to check each virtqueue for activity. Maybe there is some inefficiency doing that. >>>>>> AFAIK virtio-serial registers 64 virtqueues (on 31 ports + console) even if everything is unused. >>>>> >>>>> That could be the case if MSI is disabled. >>>> >>>> Do the windows virtio drivers enable MSIs, in their inf file? >>> >>> It depends on the version of the drivers, but it is a reasonable guess >>> at what differs between Linux and Windows. Haoyu, can you give us the >>> output of lspci from a Linux guest? >>> >> I made a test with fio on rhel-6.5 guest, the same degradation happened too, this degradation can be reproduced on rhel6.5 guest 100%. >> virtio_console module installed: >> 64K-write-sequence: 285 MBPS, 4380 IOPS >> virtio_console module uninstalled: >> 64K-write-sequence: 370 MBPS, 5670 IOPS >> >I use top -d 1 -H -p <qemu-pid> to monitor the cpu usage, and found that, >virtio_console module installed: >qemu main thread cpu usage: 98% >virtio_console module uninstalled: >qemu main thread cpu usage: 60% > I found that the statement "err = register_virtio_driver(&virtio_console);" in virtio_console module's init() function will cause the degradation, if I directly return before "err = register_virtio_driver(&virtio_console);", then the degradation disappeared, if directly return after "err = register_virtio_driver(&virtio_console);", the degradation is still there. I will try below test case, 1. Dose not emulate virito-serial deivce, then install/uninstall virtio_console driver in guest, to see whether there is difference in virtio-blk performance and cpu usage. 2. Does not emulate virito-serial deivce, then install virtio_balloon driver (and also dose not emulate virtio-balloon device), to see whether virtio-blk performance degradation will happen. 3. Emulating virtio-balloon device instead of virtio-serial deivce , then to see whether the virtio-blk performance is hampered. Base on the test result, corresponding analysis will be performed. Any ideas? Thanks, Zhang Haoyu -- 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
