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data in this table is accessible by operating systems such as VMware ESX,
Windows Server 2003 and 2008 (Windows 2000 Server does not support it) and
current Linux kernels.
These modern operating systems attempt to allocate resources that are local to
the processors being used by each process. So, when a process and its threads
start on node 1, all execution and memory access will be local to node 1. As
more processes are added to the system, the operating system balances them
across the nodes. In this case, most memory accesses are evenly distributed
across the multiple memory controllers, reducing remote access, greatly
reducing queuing delays, and improving performance.
2.6.1 Scaling VMware ESX
This section describes the NUMA features of VMware ESX 3.0.x and 3.5 as
discussed in the IBM Redbooks publication, Virtualization on the IBM System
x3950 Server, SG24-7190, available from:
http://www.redbooks.ibm.com/abstracts/sg247190.html
VMware ESX implements NUMA scheduling and memory placement policies to
manage all VMs transparently, without requiring administrators to manual
oversee the complex task of balancing VMs across multiple NUMA nodes.
VMware ESX does provide manual override controls for administrators with
advanced skills to optimize their systems to the specific requirements of their
environments.
These optimizations work seamlessly regardless of the types of guest operating
systems running. VMware ESX provides transparent NUMA support even to
guests that do not support NUMA hardware. This unique feature of VMware ESX
allows you to take advantage of cutting-edge new hardware, even when tied to
earlier operating systems.
Home nodes
VMware ESX assigns each VM a home node when the VM begins running. A VM
only runs on processors within its home node. Newly-allocated memory comes
from the home node also. Thus, if a VM's home node does not change, the VM
uses only local memory, avoiding the performance penalties associated with
remote memory accesses to other NUMA nodes. New VMs are assigned to
home nodes in a round-robin fashion. The first VM goes to the first node, the
second VM to the second node, and so on. This policy ensures that memory is
evenly used throughout all nodes of the system.
Several commodity operating systems, such as Windows 2003 Server, provide
this level of NUMA support, which is known as initial placement. It might be
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Planning, Installing, and Managing the IBM System x3950 M2
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