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NUMA(4)                FreeBSD Kernel Interfaces Manual                NUMA(4)

NAME
     NUMA - Non-Uniform Memory Access

SYNOPSIS
     options SMP
     options MAXMEMDOM=16

     #include <sys/numa.h>
     #include <sys/cpuset.h>
     #include <sys/bus.h>

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.

     NUMA is enabled when the MAXMEMDOM option is used in a kernel
     configuration file and is set to a value greater than 1.

     Thread and process NUMA policies are controlled with the
     numa_setaffinity(2) and numa_getaffinity(2) syscalls.

     The numactl(1) tool is available for starting processes with a non-
     default policy, or to change the policy of an existing thread or process.

     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.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
             numa_setaffinity(2) for more information about the available
             policies.

     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.

     The NUMA allocation policies are implemented as a policy and iterator in
     sys/vm/vm_domain.c and sys/vm/vm_domain.h.  Policy information is
     available in both struct thread and struct proc.  Processes inherit NUMA
     policy from parent processes and threads inherit NUMA policy from parent
     threads.  Note that threads do not explicitly inherit their NUMA policy
     from processes.  Instead, if no thread policy is set, the system will
     fall back to the process policy.

     For now, NUMA domain policies only influence physical page allocation in
     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.

SEE ALSO
     numactl(1), numa_getaffinity(2), numa_setaffinity(2), 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 first appeared
     in FreeBSD 11.0.

     The numactl(1) tool first appeared in FreeBSD 11.0.

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 11.1-RELEASE-p4          May 10, 2015          FreeBSD 11.1-RELEASE-p4
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