Re: [Qemu-devel] Qemu-kvm live migration modify

[Thomas Lamprecht]

hi,

this message would probably be better suited on the qemu-discuss list
not the devel.

comments inline.

On 13.04.2016 09:43, Gilar Dwitresna wrote:
> hi, 
> I have done make implementation of qemu-kvm instalation for live
> migration on ubuntu with sharing storage (NFS) configuration.
> the qemu-kvm has been succeed for live migration with default algorithm
> (guest without service), but if the guest run the service (streaming
> server), the dirty pages rate are increase from 900 to 7000 pages, and
> live migration can't succeed.
> 
> i have played run live migration with extended downtime 30 second, live
> migration can be succees, consequenly the downtime come to increase.
> My system use fast ethernet 100mbps for network bandwidth, 2 PC with ram

That's really not fast but more like the lower limit, a guest which
dirties page quickly can saturate the max 100Megabits/s / 8 = 12.5
megabyte/s line really quick. 1 Gb/s (=125 megabyte/s) would be an
better option.

> 8 GB for host, 1 PC RAM 4GB HDD 500 GB for NFS shared storage. Guest VM
> configure with 2GB RAM HDD 100 GB, migrate from host A to host B.
> 
> From some reference, if the write rate to the memory pages in use by the
> VM (here after referred to as the dirty page rate) is high compared with
> the cost of transferring the pages between the two hosts involved in the
> process, (as dictated, among others, by the network bandwidth,) then
> live migration may not be possible.
> 

With qemu 2.5 you have better autoconverge of live migration, see:
http://wiki.qemu.org/Features/AutoconvergeLiveMigration

Also post copy ram (introduced as experimental in qemu 2.5) would be an
option, see http://wiki.qemu.org/Features/PostCopyLiveMigration

cheers,
Thomas

> In the case with the high dirty pages, i run the live migration while
> the guest run the streaming server with network bandwidth 100 mbps, then
> the server can be migrated.
> 
> can i modify qemu-kvm live migration algorithm? and what should i do to
> modify this algorithm that can be migrate while the VM Guest run the
> servive (streaming server) without extended downtime?
> 
> Thanks.
> Regards, Papandayan
>