|Device Drivers Manual
NUMA — Non-Uniform
Non-Uniform Memory Access is a computer architecture design which involves unequal costs between processors, memory and IO devices in a given system.
NUMA architecture, the latency to
access specific memory or IO devices depends upon which processor the memory
or device is attached to. Accessing memory local to a processor is faster
than accessing memory that is connected to one of the other processors.
FreeBSD implements NUMA-aware memory allocation
policies. By default it attempts to ensure that allocations are balanced
across each domain. Users may override the default domain selection policy
NUMA support is enabled when the
NUMA option is specified in the kernel configuration
file. Each platform defines the
which specifies the maximum number of supported NUMA domains. This constant
may be specified in the kernel configuration file.
NUMA support can be disabled at boot time by setting
the vm.numa.disabled tunable to 1. Other values for
this tunable are currently ignored.
Thread and process
NUMA policies are
controlled with the cpuset_getdomain(2) and
cpuset_setdomain(2) syscalls. The
cpuset(1) tool is available for starting processes with a
non-default policy, or to change the policy of an existing thread or
Systems with non-uniform access to I/O devices may mark those devices with the local VM domain identifier. Drivers can find out their local domain information by calling bus_get_domain(9).
The operation of
NUMA is controlled and
exposes information with these sysctl(8) MIB
- The number of VM domains which have been detected.
- A table indicating the relative cost of each VM domain to each other. A value of 10 indicates equal cost. A value of -1 means the locality map is not available or no locality information is available.
- The map of physical memory, grouped by VM domain.
NUMA implementation is
VM-focused. The hardware
NUMA domains are mapped
into a contiguous, non-sparse VM domain space, starting from 0. Thus, VM
domain information (for example, the domain identifier) is not necessarily
the same as is found in the hardware specific information. Policy
information is available in both struct thread and struct proc.
NUMA first appeared in
FreeBSD 9.0 as a first-touch allocation policy with
a fail-over to round-robin allocation and was not configurable. It was then
modified in FreeBSD 10.0 to implement a round-robin
allocation policy and was also not configurable.
This manual page written by Adrian Chadd <adrian@FreeBSD.org>.
No statistics are kept to indicate how often
NUMA allocation policies succeed or fail.
|October 22, 2018