CPUSET Filesystem

Creating, modifying, using the cpusets can be done through the cpuset pseudo filesystem.

To mount it, type:

# mount -t cpuset none /dev/cpuset

Then under /dev/cpuset you can find a tree that corresponds to the tree of the cpusets in the system. For instance, /dev/cpuset/ is the cpuset that holds the whole system.

If you want to create a new cpuset under the top cpuset:

# cd /dev/cpuset/
# mkdir my_cpuset

Now you want to do something with this cpuset.

# cd my_cpuset

In this directory you can find several files:

# ls
cpu_exclusive  cpus  mem_exclusive  mems  notify_on_release  placement  tasks  virtualize

Reading them will give you information about the state of this cpuset: the CPUs it can use, the processes that are using it, its properties... And Writing to these files you can manipulate the cpuset.

Set some flags:

# echo 1 > notify_on_release

(Be sure to read this note about echo).
Add some cpus:

# echo 0-7 > cpus

Now attach your shell to this cpuset:

# echo $$ > tasks

You can also create cpusets inside your cpuset by using mkdir in this directory.

# mkdir my_sub_cs

To remove a cpuset, juste use rmdir:

# rmdir my_sub_cs

Note that this will fail is the cpuset is in use (has cpusets inside, or has processes attached).

Adding/removing cpus

Syntax for adding/removing cpus has been simplified. Now you just have to enter what you want to be the list of CPUs:

# echo 1-4 > cpus          -> set cpus list to cpus 1,2,3,4
# echo 1,2,3,4 > cpus      -> set cpus list to cpus 1,2,3,4

Setting flags

The syntax is very simple:

# echo 1 > cpu_exclusive       -> set flag 'cpu_exclusive'
# echo 0 > cpu_exclusive       -> unset flag 'cpu_exclusive'
# echo 1 > notify_on_release   -> set flag 'notify_on_release'

Attaching processes

To attach process with pid PID to this cpuset:

# echo PID > tasks

Note you can only attach ONE task at a time. If you have several tasks to attach, you have to do it one after another:

# echo PID1 > tasks
# echo PID2 > tasks

...

# echo PIDn > tasks

IMPORTANT NOTE:
Make sure you use a echo command that checks for errors. Some versions of /bin/echo ignore them. bash's builtin will return a non-zero error code but print no error message. You can use this macro:

echo()
{
	/bin/echo | cat
}

Thu Jan 8 15:36:43 CET 2004