Hi Bayard,
Question is how do you generate load in guest, and what's are real
bottlenecks. Generally, guest SMP maps to multiple
threads of execution for guest code, but mind page table
synchronization, device access locks and other factors adding
overhead in SMP case sometimes more severe than it would be on the real
box.
Also if your box has just 4 CPUs I wouldn't recommend assign all them to
the guest.
Thanks,
Nikolay
Bayard Bell wrote:
Anyone?
On 23 Apr 2011, at 11:50, Bayard Bell wrote:
I've got an OpenSolaris guest that I'm using as a compile server, with Mac OS X
Server as the host. I've assigned 4 CPUs to the guest, and the guest in fact
sees 4 CPUs. From the host perspective, however, what I see is that the guest
never ranges substantially above 200% (or 2 CPU) utilisation, even when the run
queue is backed up and 4 processes appear to be on the CPU. I'm comparing the
compile times to reference against other configurations, and what I'm seeing in
VirtualBox leads me to believe that I'm being presented 4 CPUs but can't
actually consume more than 2. I haven't made any apples-to-apples comparison
yet, but this nevertheless seems to be able to keep the system running under
load that can't be sustained with only 2 CPUs assigned, which seems to
indicate that the benefits of assigning more than 2 CPUs may be more about
reducing context switching and CPU migration overhead on the guest than
providing the full benefit of increased compute resources (or: IOW words the
benefit seems equivalent to provide hyperthreaded virtual CPUs rather than
cores).
Is this expected behaviour? I've looked through the documentation and wasn't
able to find any information on this. I'm running 4.0.6 and also saw this
behaviour on 4.0.4.
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