Re: [libvirt] [Qemu-devel] [PATCH v4] XBZRLE delta for live migration of large memory apps
On 08/08/2011 08:51 AM, Avi Kivity wrote:
On 08/08/2011 04:29 PM, Anthony Liguori wrote:
> One thing that strikes me about this algorithm is that
it's very good
> for a particular type of workload--shockingly good really.
Poking bytes at random places in memory is fairly generic. If you have a
lot of small objects, and modify a subset of them, this is the pattern
you get.
> I think workload aware migration compression is possible
for a lot of
> different types of workloads. That makes me a bit wary of QEMU growing
> quite a lot of compression mechanisms.
> It makes me think that this logic may really belong at a
higher level
> where more information is known about the workload. For instance, I
> can imagine XBZRLE living in something like libvirt.
A better model would be plugin based.
exec helpers are plugins. They just live in a different address space
and a channel to exchange data (pipe).
If we did .so plugins, which I'm really not opposed to, I'd want the
interface to be something like:
typedef struct MigrationTransportClass
{
ssize_t (*writev)(MigrationTransport *obj,
struct iovec *iov,
int iovcnt);
} MigrationTransportClass;
I think it's useful to use an interface like this because it makes it
easy to put the transport in a dedicated thread that didn't hold
qemu_mutex (which is sort of equivalent to using a fork'd helper but is
zero-copy at the expense of less isolation).
Regards,
Anthony Liguori