NUMA(4) FreeBSD Kernel Interfaces Manual NUMA(4)
NAME
NUMA - Non-Uniform Memory Access
SYNOPSIS
options MAXMEMDOM
options NUMA
DESCRIPTION
Non-Uniform Memory Access is a computer architecture design which
involves unequal costs between processors, memory and IO devices in a
given system.
In a 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 using cpuset(1).
NUMA support is enabled when the NUMA option is specified in the kernel
configuration file. Each platform defines the MAXMEMDOM constant, 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 process. See SMP(4) for
information about CPU to domain mapping.
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).
MIB Variables
The operation of NUMA is controlled and exposes information with these
sysctl(8) MIB variables:
vm.ndomains
The number of VM domains which have been detected.
vm.phys_locality
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.
vm.phys_segs
The map of physical memory, grouped by VM domain.
IMPLEMENTATION NOTES
The current 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.
SEE ALSO
cpuset(1), cpuset_getaffinity(2), cpuset_setaffinity(2), SMP(4),
bus_get_domain(9)
HISTORY
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.
The numa_getaffinity(2) and numa_setaffinity(2) syscalls and the
numactl(1) tool first appeared in FreeBSD 11.0 and were removed in
FreeBSD 12.0. The current implementation appeared in FreeBSD 12.0.
AUTHORS
This manual page written by Adrian Chadd <
[email protected]>.
NOTES
No statistics are kept to indicate how often NUMA allocation policies
succeed or fail.
FreeBSD 14.1-RELEASE-p8 October 22, 2018 FreeBSD 14.1-RELEASE-p8