MPO Observability Tools
The organization of the lgroup hierarchy simplifies the task of finding the nearest resources
in the system. Each thread is assigned a home lgroup upon creation. The operating system
attempts to allocate resources for the thread from the thread's home lgroup by default. For
example, the Oracle Solaris kernel attempts to schedule a thread to run on the CPUs in the
thread's home lgroup and allocate the thread's memory in the thread's home lgroup by default.
If the desired resources are not available from the thread's home lgroup, the kernel can traverse
the lgroup hierarchy to find the next nearest resources from parents of the home lgroup. If the
desired resources are not available in the home lgroup's parents, the kernel continues to traverse
the lgroup hierarchy to the successive ancestor lgroups of the home lgroup. The root lgroup is
the ultimate ancestor of all other lgroups in a system and contains all of the system's resources.
The Memory Placement Optimization (MPO) tools enable developers to tune the performance
of the MPO features in cases where the default MPO behaviors do not yield the desired
performance.
The lgroup APIs export the lgroup abstraction for applications to use for observability and
performance tuning. A new library, called liblgrp, contains the new APIs. Applications can
use the APIs to perform the following tasks:
■
Traverse the group hierarchy
■
Discover the contents and characteristics of a given lgroup
■
Affect the thread and memory placement on lgroups
MPO Observability Tools
The MPO tools help developers to answer questions about system configuration and balance or
placement. The tools also provide the basic information and mechanisms that developers need
in order to determine whether MPO is successful and to diagnose problems related to MPO.
To determine the degree of success that MPO has in providing useful locality assignments and
acceptable performance, it is important to know a given thread's affinities for lgroups, including
its home lgroup, and where the thread's memory is allocated.
The MPO observability tools provide developers with the ability to determine the actions taken
by the system. The MPO thread and memory placement tools enable developers to act on that
information. Developers can also use the dtrace(1M) tool to gain further insights into the
system's behavior.
12 Memory and Thread Placement Optimization Developer's Guide • December 2018
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