Virtual Ethernet - IBM p5 590 System Handbook

A mix of dedicated and shared processors within the same partition is not
supported.
If you dynamically remove a virtual processor you cannot specify a particular
virtual CPU to be removed. The operating system will choose the virtual CPU
to be removed.
Shared processors may render AIX 5L affinity management useless. AIX will
continue to utilize affinity domain information as provided by firmware to build
associations of virtual processors to memory, and will continue to show
preference to redispatching a thread to the virtual CPU that it last ran on.
Operating systems and applications running in shared partitions need not be
aware that they are sharing processors. However, overall system performance
can be significantly improved by minor operating system changes.
In a shared partition, there is not a fixed relationship between the virtual
processor and the physical processor. The POWER Hypervisor will try to use a
physical processor with the same memory affinity as the virtual processor, but it
is not guaranteed. Virtual processors have the concept of a home physical
processor. If it can't find a physical processor with the same memory affinity, then
it gradually broadens its search to include processors with weaker memory
affinity, until it finds one that it can use. As a consequence, memory affinity is
expected to be weaker in shared processor partitions.
Workload variability is also expected to be increased in shared partitions,
because there are latencies associated with the scheduling of virtual processors
and interrupts. Simultaneous multi-threading may also increase variability, since
it adds another level of resource sharing, which could lead to a situation where
one thread interferes with the forward progress of its sibling.
If an application is cache sensitive or cannot tolerate variability, then the
dedicated partition with simultaneous multi-threading disabled is recommended.
In dedicated partitions, the entire processor is assigned to a partition. Processors
are not shared with other partitions, and they are not scheduled by the POWER
Hypervisor. Dedicated partitions must be explicitly created by the system
administrator using the HMC.

3.3 Virtual Ethernet

Virtual Ethernet enables inter-partition communication without the need for
physical network adapters assigned to each partition. Virtual Ethernet allows the
administrator to define in-memory point-to-point connections between partitions.
These connections exhibit similar characteristics as physical high-bandwidth
Ethernet connections and supports multiple protocols (IPv4, IPv6, ICMP). Virtual
Chapter 3. POWER5 virtualization capabilities
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