Re: [Qemu-devel] Stalls on Live Migration of VMs with a lot of memory

[Peter Lieven]

On 04.01.2012 02:38, Shu Ming wrote:
> On 2012-1-4 2:04, Peter Lieven wrote:
> > Hi all,
> >
> > is there any known issue when migrating VMs with a lot of (e.g. 32GB) 
> > of memory.
> > It seems that there is some portion in the migration code which takes 
> > too much time when the number
> > of memory pages is large.
> >
> > Symptoms are: Irresponsive VNC connection, VM stalls and also 
> > irresponsive QEMU Monitor (via TCP).
> >
> > The problem seems to be worse on 10G connections between 2 Nodes (i 
> > already tried limiting the
> > bandwidth with the migrate_set_speed command) than on 1G connections.
> Is the migration  accomplished finally? How long will that be?  I did 
> a test on VM with 4G and it took me about two seconds.
it seems that the majority of time (90%) is lost in:

cpu_physical_memory_reset_dirty(current_addr,
                                            current_addr + 
TARGET_PAGE_SIZE,
                                            MIGRATION_DIRTY_FLAG);

anyone any idea, to improve this?