PLGRP(1)PLGRP(1)NAMEplgrp - observe and affect home lgroup and lgroup affinities of threads
SYNOPSISplgrp [-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
DESCRIPTIONplgrp 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 hier‐
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
The different levels of lgroup affinities and their semantics are fully
described in lgrp_affinity_set(3LGRP).
lgroup_list is a comma separated list of one or more of the following:
- Range of lgroup_IDs specified as
<start lgroup_ID>-<end lgroup_ID>
The all keyword represents all lgroup IDs in the system. The root key‐
word represents the ID of the root lgroup. The leaves keyword repre‐
sents the IDs of all leaf lgroups, that is, lgroups which do not have
Specifying Processes and Threads
plgrp takes one or more space separated processes or threads as argu‐
ments. Processes and threads can be specified in a manner similiar 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:
Display lgroup affinities of specified processes or threads for the
-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.
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 $$
Example 2 Setting the Home lgroup of Multiple Threads to the Root
The following example sets the home lgroup of multiple threads to the
% 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
PID/LWPID HOME AFFINITY
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
PID/LWPID HOME AFFINITY
101398/1 1 => 2 0,2/none => 2/strong,0/weak
The following exit values are returned:
Syntax error. Nothing was changed.
Non-fatal error or interrupt. Something might have changed.
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ See below. │
The command syntax is Unstable. The output formats are Unstable.
SEE ALSOlgrpinfo(1), madv.so.1(1), pmadvise(1), pmap(1), proc(1), ps(1),
prstat(1M), lgrp_affinity_get(3LGRP), lgrp_affinity_set(3LGRP),
lgrp_home(3LGRP), liblgrp(3LIB), proc(4), attributes(5)WARNINGS
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:
and looking for a T in the first column of the output. Certain pro‐
cesses, for example, sched, can show the T status by default most of
Sep 8, 2006 PLGRP(1)