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Re: [Qemu-devel] [question] virtio-blk performancedegradationhappened wi
From: |
Zhang Haoyu |
Subject: |
Re: [Qemu-devel] [question] virtio-blk performancedegradationhappened with virito-serial |
Date: |
Thu, 4 Sep 2014 10:20:53 +0800 |
>> >>> 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.
>> >>
>> >I don't think so,
>> >I use iometer to test 64k-read(or write)-sequence case, if I disable the
>> >virtio-serial dynamically via device manager->virtio-serial => disable,
>> >then the performance get promotion about 25% immediately, then I re-enable
>> >the virtio-serial via device manager->virtio-serial => enable,
>> >the performance got back again, very obvious.
>> add comments:
>> Although the virtio-serial is enabled, I don't use it at all, the
>> degradation still happened.
>
>Using the vectors= option as mentioned below, you can restrict the
>number of MSI vectors the virtio-serial device gets. You can then
>confirm whether it's MSI that's related to these issues.
>
I use "-device virtio-serial,vectors=4" instead of "-device virtio-serial", but
the degradation still happened, nothing changed.
with virtio-serial enabled:
64k-write-sequence: 4200 IOPS
with virtio-serial disabled:
64k-write-sequence: 5300 IOPS
How to confirm whether it's MSI in windows?
Thanks,
Zhang Haoyu
>> >So, I think it has no business with legacy interrupt mode, right?
>> >
>> >I am going to observe the difference of perf top data on qemu and perf kvm
>> >stat data when disable/enable virtio-serial in guest,
>> >and the difference of perf top data on guest when disable/enable
>> >virtio-serial in guest,
>> >any ideas?
>> >
>> >Thanks,
>> >Zhang Haoyu
>> >>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?
- Re: [Qemu-devel] [question] virtio-blk performance degradationhappenedwith virito-serial, (continued)
- Re: [Qemu-devel] [question] virtio-blk performance degradationhappenedwith virito-serial, Zhang Haoyu, 2014/09/07
- Re: [Qemu-devel] [question] virtio-blk performance degradationhappenedwith virito-serial, Amit Shah, 2014/09/11
- Re: [Qemu-devel] [question] virtio-blk performance degradation happened with virito-serial, Zhang Haoyu, 2014/09/11
- Re: [Qemu-devel] [question] virtio-blk performance degradation happened with virito-serial, Stefan Hajnoczi, 2014/09/12
- Re: [Qemu-devel] [question] virtio-blk performance degradation happened with virito-serial, Max Reitz, 2014/09/13
- Re: [Qemu-devel] [question] virtio-blk performance degradation happened with virito-serial, Zhang Haoyu, 2014/09/16
Re: [Qemu-devel] [question] virtio-blk performance degradationhappened with virito-serial, Amit Shah, 2014/09/02
Re: [Qemu-devel] [question] virtio-blk performancedegradationhappened with virito-serial,
Zhang Haoyu <=
Re: [Qemu-devel] [question] virtio-blk performance degradationhappened with virito-serial, Fam Zheng, 2014/09/19
Re: [Qemu-devel] [question] virtio-blk performance degradationhappened with virito-serial, Paolo Bonzini, 2014/09/19
Re: [Qemu-devel] [question] virtio-blk performancedegradationhappened with virito-serial, Zhang Haoyu, 2014/09/22
Re: [Qemu-devel] [question] virtio-blk performancedegradationhappened with virito-serial, Fam Zheng, 2014/09/22