68 Planning, Installing, and Managing the IBM System x3950 M2data in this table is accessible by operating systems such as VMware ESX,Windows Server 2003 and 2008 (Windows 2000 Server does not support it) andcurrent Linux kernels.These modern operating systems attempt to allocate resources that are local tothe processors being used by each process. So, when a process and its threadsstart on node 1, all execution and memory access will be local to node 1. Asmore processes are added to the system, the operating system balances themacross the nodes. In this case, most memory accesses are evenly distributedacross the multiple memory controllers, reducing remote access, greatlyreducing queuing delays, and improving performance.2.6.1 Scaling VMware ESXThis section describes the NUMA features of VMware ESX 3.0.x and 3.5 asdiscussed in the IBM Redbooks publication, Virtualization on the IBM Systemx3950 Server, SG24-7190, available from:http://www.redbooks.ibm.com/abstracts/sg247190.htmlVMware ESX implements NUMA scheduling and memory placement policies tomanage all VMs transparently, without requiring administrators to manualoversee the complex task of balancing VMs across multiple NUMA nodes.VMware ESX does provide manual override controls for administrators withadvanced skills to optimize their systems to the specific requirements of theirenvironments.These optimizations work seamlessly regardless of the types of guest operatingsystems running. VMware ESX provides transparent NUMA support even toguests that do not support NUMA hardware. This unique feature of VMware ESXallows you to take advantage of cutting-edge new hardware, even when tied toearlier operating systems.Home nodesVMware ESX assigns each VM a home node when the VM begins running. A VMonly runs on processors within its home node. Newly-allocated memory comesfrom the home node also. Thus, if a VM’s home node does not change, the VMuses only local memory, avoiding the performance penalties associated withremote memory accesses to other NUMA nodes. New VMs are assigned tohome nodes in a round-robin fashion. The first VM goes to the first node, thesecond VM to the second node, and so on. This policy ensures that memory isevenly used throughout all nodes of the system.Several commodity operating systems, such as Windows 2003 Server, providethis level of NUMA support, which is known as initial placement. It might be
