PLGRP(1) User Commands PLGRP(1)


plgrp - observe and affect home lgroup and lgroup affinities of threads


plgrp [-F] [-h] pid | core [/lwps] ...

plgrp [-F] -a lgroup_list pid[/lwps] ...

plgrp [-F] -H lgroup_list pid[/lwps] ...

plgrp [-F] -A lgroup_list/none | weak |strong [,...] pid
[/lwps] ...


plgrp displays or sets the home lgroup and lgroup affinities for one or
more processes, threads, or LWPs.

An lgroup represents the set of CPU and memory-like hardware devices that
are at most some distance (latency) apart from each other. Each lgroup in
the system is identified by a unique lgroup ID. The lgroups are organized
into a hierarchy to facilitate finding the nearest resources (see
lgrpinfo(1) for more about lgroups and the lgroup hierarchy).

By default, each thread is assigned a home lgroup upon creation. When the
system needs to allocate a CPU or memory resource for a thread, it
searches the lgroup hierarchy from the thread's home lgroup for the
nearest available resources to the thread's home.

Typically, the home lgroup for a thread is the lgroup for which the
thread has the most affinity. Initially, the system chooses a home lgroup
for each thread, but leaves the thread's affinity for that lgroup set to
none. If a thread sets a stronger affinity for an lgroup in its processor
set other than its home, the thread is rehomed to that lgroup as long as
the thread is not bound to a CPU. The thread can be re-homed to the
lgroup in its processor set with the next highest affinity when the
affinity (if any) for its home lgroup is removed (set to none).

The different levels of lgroup affinities and their semantics are fully
described in lgrp_affinity_set(3LGRP).


Specifying lgroups

lgroup_list is a comma separated list of one or more of the following:

- lgroup_ID
- Range of lgroup_IDs specified as
<start lgroup_ID>-<end lgroup_ID>
- all
- root
- leaves

The all keyword represents all lgroup IDs in the system. The root keyword
represents the ID of the root lgroup. The leaves keyword represents the
IDs of all leaf lgroups, that is, lgroups which do not have any children.

Specifying Processes and Threads

plgrp takes one or more space separated processes or threads as
arguments. Processes and threads can be specified in a manner similar to
the proc(1) tools. A process ID may be specified as an integer pid or
/proc/pid. Shell expansions can be used to specify processes when
/proc/pid is used. For example, /proc/* can be used to specify all the
processes in the system. If a process ID is given alone, then all the
threads of the process are included as arguments to plgrp.

A thread can be explicitly specified with its process ID and thread ID
given together as pid/lwpid. Multiple threads of a process can be
selected at once by using the hyphen (-) and comma(,). For example,
pid/1,2,7-9 specifies threads 1, 2, 7, 8, and 9 of the process with pid
as its process ID.


The following options are supported:

-a lgroup_list

Display lgroup affinities of specified processes or threads for the
specified lgroup_list.

-A lgroup_list/none|weak|strong [,...]

Set affinity of specified processes or threads for the specified

A comma separated list of lgroups/affinity assignments can be given
to set several affinities at once.


Force by grabbing the target process even if another process has
control. Caution should be exercised when using the -F flag.
Imposing two controlling processes on one victim process can lead to
chaos. Safety is assured only when the primary controlling process
(typically a debugger) has stopped the victim process, but isn't
doing anything during the application of this proc tool. See WARNINGS
for more details.


Get home lgroup of specified processes and/or threads. If no options
are specified, this is the default.

-H lgroup_list

Set home lgroup of specified processes and threads.

This sets a strong affinity for the desired lgroup to rehome the
threads. If more than one lgroup is specified, plgrp tries to home
the threads to the lgroups in a round robin fashion.


The following operands are supported:

Specifies thread. See USAGE.

Specifies process ID. See USAGE.


Example 1: Getting the Home lgroup for the Shell

The following example gets the home lgroup for the shell:

% plgrp $$
3401/1 1

Example 2: Setting the Home lgroup of Multiple Threads to the Root lgroup

The following example sets the home lgroup of multiple threads to the
root lgroup:

% plgrp -H root `pgrep firefox`
918/1 1 => 0
934/1 2 => 0
934/2 1 => 0
934/3 2 => 0
934/625 1 => 0
934/626 2 => 0
934/624 2 => 0
934/623 2 => 0
934/630 1 => 0

Example 3: Getting Two Threads' Affinities for lgroups 0-2

The following example gets two threads' affinities for lgroups 1-2:

% plgrp -a 0-2 101398/1 101337/1
101398/1 1 0-2/none
101337/1 1 0-2/none

Example 4: Setting lgroup Affinities

The following example sets lgroup affinities:

% plgrp -A 0/weak,1/none,2/strong 101398
101398/1 1 => 2 0,2/none => 2/strong,0/weak


The following exit values are returned:

Successful completion.

Syntax error. Nothing was changed.

Non-fatal error or interrupt. Something might have changed.


See attributes(7) for descriptions of the following attributes:

|Interface Stability | See below. |

The command syntax is Unstable. The output formats are Unstable.


lgrpinfo(1),, pmadvise(1), pmap(1), proc(1), ps(1),
lgrp_affinity_get(3LGRP), lgrp_affinity_set(3LGRP), lgrp_home(3LGRP),
liblgrp(3LIB), proc(5), attributes(7), prstat(8)


Like the proc(1) tools, the plgrp utility stops its target processes
while inspecting them and reports the results when invoked with any

There are conditions under which processes can deadlock. A process can do
nothing while it is stopped. Stopping a heavily used process in a
production environment (even for a short amount of time) can cause severe
bottlenecks and even hangs of these processes, making them to be
unavailable to users. Thus, stopping a UNIX process in a production
environment should be avoided. See proc(1).

A process that is stopped by this tool might be identified by issuing the
following command:

/usr/bin/ps -eflL

and looking for a T in the first column of the output. Certain processes,
for example, sched, can show the T status by default most of the time.

illumos April 9, 2016 PLGRP(1)