Re: [Xen-devel] HYBRID: PV in HVM container

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Thu, 2011-07-28 at 12:34 +0100, Stefano Stabellini wrote:
> On Thu, 28 Jul 2011, Mukesh Rathor wrote:
> > Hi folks,
> > 
> > Well, I did some benchmarking and found interesting results. Following
> > runs are on a westmere with 2 sockets and 10GB RAM.  Xen was booted
> > with maxcpus=2 and entire RAM. All guests were started with 1vcpu and 2GB 
> > RAM. dom0 started with 1 vcpu and 704MB. Baremetal was booted with 2GB 
> > and 1 cpu.  HVM guest has EPT enabled. HT is on.
> > 
> > So, unless the NUMA'ness interfered with results (using some memory on 
> > remote socket), it appears HVM does very well. To the point that it
> > seems a hybrid is not going to be worth it. I am currently running
> > tests on a single socket system just to be sure.
> > 
> 
> The high level benchmarks I run to compare PV and PV on HVM guests show
> a very similar scenario.
> 
> It is still worth having HYBRID guests (running with EPT?) in order to
> support dom0 in an HVM container one day not too far from now.

I think it is also worth bearing in mind that once we have basic support
for HYBRID we can begin looking at/measuring which hardware features
offer advantages to PV guests and enhancing the PV interfaces for use by
HYBRID guests etc. (i.e. make things truly hybrid PV+Hardware and not
just contained PV)

Also there are arguments to be made for HYBRID over PVHVM in terms of
ease of manageability (i.e. a lot of folks like the dom0-supplied kernel
idiom which PV enables), avoiding the need for a virtualised BIOS and
emulated boot paths, HYBRID can potentially give a best of both in the
trade off between standard-PV vs. HVM/PVHVM while also not needing a
QEMU process for each guest (which helps scalability and so on) etc. I
think HYBRID is worthwhile even if it is basically on-par with PVHVM for
some workloads.

Ian.


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