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

[Stefan Hajnoczi]

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