xref: /freebsd/share/man/man4/numa.4 (revision 6520495abc109aa5af083b7cde70e4cf9c338de0)

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.Dd May 10, 2015
.Dt NUMA 4
.Os
.Sh NAME
.Nm NUMA
.Nd Non-Uniform Memory Access
.Sh SYNOPSIS
.Cd options SMP
.Cd options MAXMEMDOM=16
.Pp
.In sys/numa.h
.In sys/cpuset.h
.In sys/bus.h
.Sh DESCRIPTION
Non-Uniform Memory Access is a computer architecture design which
involves unequal costs between processors, memory and IO devices
in a given system.
.Pp
In a
.Nm
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.
.Pp
.Nm
is enabled when the
.Cd MAXMEMDOM
option is used in a kernel configuration
file and is set to a value greater than 1.
.Pp
Thread and process
.Nm
policies are controlled with the
.Xr numa_setaffinity 2
and
.Xr numa_getaffinity 2
syscalls.
.Pp
The
.Xr numactl 1
tool is available for starting processes with a non-default
policy, or to change the policy of an existing thread or process.
.Pp
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
.Xr bus_get_domain 9 .
.Ss MIB Variables
The operation of
.Nm
is controlled and exposes information with these
.Xr sysctl 8
MIB variables:
.Pp
.Bl -tag -width indent -compact
.It Va vm.ndomains
The number of VM domains which have been detected.
.Pp
.It Va vm.default_policy
The default VM domain allocation policy.
Defaults to "first-touch-rr".
The valid values are "first-touch", "first-touch-rr",
"rr", where "rr" is a short-hand for "round-robin."
See
.Xr numa_setaffinity 2
for more information about the available policies.
.Pp
.It Va 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.
.Pp
.It Va vm.phys_segs
The map of physical memory, grouped by VM domain.
.El
.Sh IMPLEMENTATION NOTES
The current
.Nm
implementation is VM-focused.
The hardware
.Nm
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.
.Pp
The
.Nm
allocation policies are implemented as a policy and iterator in
.Pa sys/vm/vm_domain.c
and
.Pa sys/vm/vm_domain.h .
Policy information is available in both struct thread and struct proc.
Processes inherit
.Nm
policy from parent processes and threads inherit
.Nm
policy from parent threads.
Note that threads do not explicitly inherit their
.Nm
policy from processes.
Instead, if no thread policy is set, the system
will fall back to the process policy.
.Pp
For now,
.Nm
domain policies only influence physical page allocation in
.Pa sys/vm/vm_phys.c .
This is useful for userland memory allocation, but not for kernel
and driver memory allocation.
These features will be implemented in future work.
.Sh SEE ALSO
.Xr numactl 1 ,
.Xr numa_getaffinity 2 ,
.Xr numa_setaffinity 2 ,
.Xr bus_get_domain 9
.Sh HISTORY
.Nm
first appeared in
.Fx 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
.Fx 10.0
to implement a round-robin allocation policy and was also not configurable.
.Pp
The
.Xr numa_getaffinity 2
and
.Xr numa_setaffinity 2
syscalls first appeared in
.Fx 11.0 .
.Pp
The
.Xr numactl 1
tool first appeared in
.Fx 11.0 .
.Sh AUTHORS
This manual page written by
.An Adrian Chadd Aq Mt adrian@FreeBSD.org .
.Sh NOTES
No statistics are kept to indicate how often
.Nm
allocation policies succeed or fail.