Viewing: cpu_partition_distance.4
.TH CPU_PARTITION_DISTANCE 4 2026-03-31 Lustre "Lustre Kernel Interfaces"
.SH NAME
cpu_partition_distance \- show NUMA distance between CPTs
.SH SYNOPSIS
.SS PROPERTIES
.TP
.B Access Permissions
.br
.BR 444 " | " -r--r--r--
.TP
.B Scope
.br
Global
.TP
.B Config
.br
Always present
.SH DESCRIPTION
.B cpu_partition_distance
shows the maximum NUMA distance between all source nodes to all destination
nodes in each partition. The distance values are used to determine the best
network interface for each thread to use when sending messages,
in order to minimize cross-NUMA memory access.
The NUMA distance reported between two nodes the ratio of the latency to access
memory on the destination node from the source node compared to that of
accessing local memory, the values are normalized to 10 (1.0x) meaning that if
the distance between two nodes is
.IR DIST ,
then there will be
.RI ( DIST /10)x
more latency to access remote memory.
These values are taken from `/sys/devices/system/node/*/distance`
parameters provided by the kernel.
.PP
The distance output is formatted as follows:
.EX
CPT0 : CPT0:DIST00 CPT1:DIST01 ...
CPT1 : CPT0:DIST10 CPT1:DIST11 ...
\&...
.EE
.SH MODULES
This parameter is in the following modules:
.EX
.B cpu_partition_distance
.EE
.SH EXAMPLES
For a system with 4 partitions:
.RS
.EX
.RB # " lctl get_param cpu_partition_distance"
cpu_partition_distance=
0 : 0:10 1:12 2:10 3:11
1 : 0:12 1:10 2:14 3:10
2 : 0:10 1:14 2:10 3:11
3 : 0:11 1:10 2:11 3:10
.EE
.RE
.SH AVAILABILITY
.B cpu_partition_distance
is part of the
.BR lustre (7)
filesystem package since release 2.10.0.
.\" Added in commit v2_9_52_0-6-gdef25e9c7e
.SH SEE ALSO
.BR cpu_npartitions (4),
.BR cpu_partition_distance (4),
.BR cpu_partition_table (4),
.BR numa (7)
