Re: [Qemu-devel] qemu vm big network latency when met heavy io

[Stefan Hajnoczi <stefanha@gmail.com>]

On Mon, Jan 06, 2014 at 02:55:54PM +0800, 叶绍琛 wrote:
> 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.

Does this mean you are comparing QEMU's rbd block driver against the
Linux kernel rbd driver?

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

Please try running jitterd to confirm that the guest vCPU is getting
sufficient execution time:
http://codemonkey.ws/cgit/jitterd.git/tree/jitterd.c

This test will confirm that network I/O is performing poorly, not a
starved guest CPU.

> 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 
> 
> 
> ------------------
> Alan Ye