illumos: manual page: lgrp

LGRP_LATENCY(3LGRP) Locality Group Library Functions LGRP_LATENCY(3LGRP)

NAME

lgrp_latency, lgrp_latency_cookie - get latency between two lgroups

SYNOPSIS

cc [ flag... ] file... -llgrp [ library... ]
#include <sys/lgrp_user.h>

int lgrp_latency_cookie(lgrp_cookie_t cookie, lgrp_id_t from,
lgrp_id_t to, lgrp_lat_between_t between);

int lgrp_latency(lgrp_id_t from, lgrp_id_t to);

DESCRIPTION

The lgrp_latency_cookie() function takes a cookie representing a snapshot
of the lgroup hierarchy obtained from lgrp_init(3LGRP) and returns the
latency value between a hardware resource in the from lgroup to a
hardware resource in the to lgroup. If from is the same lgroup as to, the
latency value within that lgroup is returned.

The between argument should be set to the following value to specify
between which hardware resources the latency should be measured:

LGRP_LAT_CPU_TO_MEM /* latency from CPU to memory */

The latency value is defined by the operating system and is platform-
specific. It can be used only for relative comparison of lgroups on the
running system. It does not necessarily represent the actual latency
between hardware devices, and it might not be applicable across
platforms.

The lgrp_latency() function is similar to the lgrp_latency_cookie()
function, but returns the latency between the given lgroups at the given
instant in time. Since lgroups can be freed and reallocated, this
function might not be able to provide a consistent answer across calls.
For that reason, the lgrp_latency_cookie() function should be used in its
place.

RETURN VALUES

Upon successful completion, the latency value is returned. Otherwise -1
is returned and errno is set to indicate the error.

ERRORS

The lgrp_latency_cookie() and lgrp_latency() functions will fail if:

EINVAL
The specified cookie, lgroup ID, or value given for the between
argument is not valid.

ESRCH
The specified lgroup ID was not found, the from lgroup does not
contain any CPUs, or the to lgroup does not have any memory.