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
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
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 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 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 pro-
cesses when /proc/pid is used. For example, /proc/* can be used to specify all the pro-
cesses 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 specified
Set affinity of specified processes or threads for the specified lgroup_list.
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 any-
thing 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
The following operands are supported:
lwps Specifies thread. See USAGE.
pid 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 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
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:
0 Successful completion.
1 Syntax error. Nothing was changed.
2 Non-fatal error or interrupt. Something might have changed.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Availability |SUNWesu |
|Interface Stability |See below. |
The command syntax is Unstable. The output formats are Unstable.
lgrpinfo(1), madv.so.1(1), pmadvise(1), pmap(1), proc(1), ps(1), prstat(1M), lgrp_affin-
ity_get(3LGRP), lgrp_affinity_set(3LGRP), lgrp_home(3LGRP), liblgrp(3LIB), proc(4),
Like the proc(1) tools, the plgrp utility stops its target processes while inspecting them
and reports the results when invoked with any option.
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 com-
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.
SunOS 5.11 8 Sep 2006 plgrp(1)