[Qemu-discuss] qemu vm big network latency when met heavy io

[??????]

hi, all:

There is a problem when I use ceph rbd for qemu storage. I launch 4 virtual machines, and start 5G random write test at the same time. Under such heavy I/O, the network to 

virtual machine almost unusable, the network latency is extremely big.

I had test another situation, when I use 'virsh attach-device' command to attach rbd which mapped in my host machine(which run virtual machines), the problem was not show again.

So, I think this must be qemu-rbd 's problem.

Here is my testing environment:

# virsh version

Compiled against library: libvirt 1.2.0

Using library: libvirt 1.2.0

Using API: QEMU 1.2.0

Running hypervisor: QEMU 1.7.0

In vm's xml, I define the rbd like this:

    <disk type='network' device='disk'>

      <driver name='qemu' type='raw' cache='none'/>

      <source protocol='rbd' name='qemu/rbd-vm4'>

        <host name='10.120.111.111' port='6789'/>

      </source>

      <auth username='libvirt'>

        <secret type='ceph' uuid='38b66185-4117-47a6-90bd-64111c3fc5d2'/>

      </auth>

      <target dev='vdb' bus='virtio'/>

      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>

    </disk>

testing tool is : fio

io depth is : 32

io engine is : libaio

io direct is open

Is there anyone met such a problem? 

regards

Alan Ye 

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Alan Ye