Locality-Optimized Resource Alignment

Table 4. Values for the numa_policy tunable parameter

Value

Default Memory Allocation Policy

Use Cases

0 automatically selected by the kernel at boot time recommended for all common workloads

and configurations

1 from the locality closest to the allocating processor in LORA mode or with lots of local

memory configured

2 from interleaved memory in SMP mode or with lots of interleaved

memory configured

3 text and library data segments from interleaved memory; others from

the locality closest to the allocating processor

highly threaded applications exhibiting

spatial locality

4 private objects from the closest locality; shared objects from

interleaved memory

applications that access lots of global

data

mpsched command

In LORA mode, the kernel attempts to provide good alignment between the processors executing an

application and the memory that they reference. To offer direct control over process placement, HP-

UX 11i provides the mpsched command. The command reveals information about localities in the

system and controls the processor or locality on which a specific process executes. The man page

has the full details on how to use the command.

The mpsched command can be used to bind processes to a particular locality. In the absence of this

binding, the operating system might schedule processes in different localities as the workload ebbs

and flows. The binding ensures that the processes are always executing in the same locality as the

memory they allocate and hence will experience low memory latency. The command can also be

used to specify a launch policy to control the scheduling of children forked by a process.

Using mpsched to enforce good alignment for Java

HP-UX is usually able to achieve good alignment when running Java. Here are some guidelines for

explicit tunes to enforce good alignment when running multiple instances of the Java virtual machine.

We'll assume that each Java instance is small enough in terms of processor and memory resources to

fit into a single locality. It is best to subdivide the Java instance if it exceeds the capacity of a single

locality.

Use the command mpsched –s to determine the number of localities in the partition and the locality

identifier corresponding to each locality. It is usually not necessary to use any launch policy if there

are fewer than three localities in the partition. If there are many localities, use commands similar to

the following to launch Java, distributing the Java virtual machines instances evenly across two

localities:

mpsched –l 2 java

mpsched –l 3 java

Since Java is highly threaded, it may be beneficial to set the numa_policy parameter to 3.