3 Full Featured Cpuset Manipulation Commands #
While basic shielding as described above is useful and a common use model
for cset, there comes a time when more functionality
will be desired to implement your strategy. To implement this,
cset provides two subcommands: set,
which allows you to manipulate cpusets; and proc, which
allows you to manipulate processes within those cpusets.
3.1 The set Subcommand #
To do anything with cpusets, you must be able to create, adjust,
rename, move, and destroy them. The set subcommand
allows the management of cpusets in such a manner.
3.1.1 Creating and Destroying Cpusets with set #
The basic syntax of set for cpuset creation is:
tux >csetset -c 1-3 -s my_cpuset1 cset: --> created cpuset "my_cpuset1"
This creates a cpuset named my_cpuset1 with a CPUSPEC
of CPU1, CPU2 and CPU3. The CPUSPEC is the same concept as described in
the Section 2.2, “Setup and Teardown of the Shield”. The
set subcommand also takes a -m/--mem
option that lets you specify the memory nodes the set
will use and flags to make the CPUs and MEMs exclusive to the
cpuset. If you are on a non-NUMA machine, leave the
-m option out and the default memory node
0 will be used.
Like with shield, you can adjust the CPUs and
MEMs with subsequent calls to set. If, for example, you want to adjust
the my_cpuset1 cpuset to only use CPUs 1 and 3 (and
omit CPU2), then issue the following command.
tux >csetset -c 1,3 -s my_cpuset1 cset: --> modified cpuset "my_cpuset
cset will then adjust the CPUs that are assigned to
the my_cpuset1 set to only use CPU1 and CPU3.
To rename a cpuset, use the -n/--newname option. For
example:
tux >csetset -s my_cpuset1 -n super_set cset: --> renaming "/cpusets/my_cpuset1" to "super_set"
Renames the cpuset called my_cpuset1 to
super_set.
To destroy a cpuset, use the -d/--destroy option as
follows.
tux >csetset -d super_set cset: --> processing cpuset "super_set", moving 0 tasks to parent "/"... cset: --> deleting cpuset "/super_set" cset: done
This command destroys the newly created cpuset called
super_set. When a cpuset is destroyed, all the tasks
running in it are moved to the parent cpuset. The root cpuset, which
always exists and always contains all CPUs, cannot be destroyed. You may
also give the --destroy option a list of cpusets to
destroy.
The cset subcommand creates the cpusets based on a
mounted cpuset file system. You do not need to know where that file
system is mounted, although it is easy to figure out (by default it is
on /cpusets). When you give the
set subcommand a name for a new cpuset, it is
created wherever the cpuset file system is mounted.
To create a cpuset hierarchy, then you must give a path to
the cset set subcommand. This path will always begin
with the root cpuset, for which the path is /. For
example:
tux >csetset -c 1,3 -s top_set cset: --> created cpuset "top_set"tux >csetset -c 3 -s /top_set/sub_set cset: --> created cpuset "/top_set/sub_set"
These commands created two cpusets: top_set and
sub_set. The top_set uses CPU1 and
CPU3. It has a subset of sub_set which only uses
CPU3. Once you have created a subset with a path, then if the name is
unique, you do not need to specify the path to affect it. If
the name is not unique, then cset will complain and
ask you to use the path. For example:
tux >csetset -c 1,3 -s sub_set cset: --> modified cpuset "sub_set
This command adds CPU1 to the sub_set cpuset for its
use. Note that using the path in this case is optional.
If you attempt to destroy a cpuset which has sub-cpusets,
cset will complain and not do it unless you use the
-r/--recurse and the --force options.
If you do use --force, then all the tasks running in
all subsets of the deletion target cpuset will be moved to the
target’s parent cpuset and all cpusets.
Moving a cpuset from under a certain cpuset to a different location is not implemented.
3.1.2 Listing Cpusets with set #
To list cpusets, use the set subcommand with the
-l/--list option. For example:
tux >csetset -l cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 320 1 / one 3 n 0 n 0 1 /one
This shows that there is currently one cpuset present called
one. (Of course there is also the
root set, which is always present.) The output shows
that the one cpuset has no tasks running in it. The
root cpuset has 320 tasks running. The
-X for CPUs and MEMs fields denotes whether the CPUs
and MEMs in the cpusets are marked exclusive to those cpusets. Note that
the one cpuset has subsets as indicated by a
1 in the Subs field. You can
specify a cpuset to list with the set subcommand as
follows:
tux >csetset -l -s one cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- one 3 n 0 n 0 1 /one two 3 n 0 n 0 1 /one/two
This output shows that there is a cpuset called two
in cpuset one and it also has subset. You can also
ask for a recursive listing as follows:
tux >csetset -l -r cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 320 1 / one 3 n 0 n 0 1 /one two 3 n 0 n 0 1 /one/two three 3 n 0 n 0 0 /one/two/three
This command lists all cpusets existing on the system since it asks for
a recursive listing beginning at the root cpuset.
Incidentally, should you need to specify the root
cpuset you can use either root or
/ to specify it explicitly—just remember that the
root cpuset cannot be deleted or modified.
3.2 The proc Subcommand #
Now that you know how to create, rename and destroy cpusets with the
set subcommand, the next step is to manage threads and
processes in those cpusets. The subcommand to do this is called
proc and it allows you to exec processes into a
cpuset, move existing tasks around existing cpusets, and list tasks
running in specified cpusets. For the following examples, let us assume a
cpuset setup of two sets as follows:
tux >csetset -l cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 309 2 / two 2 n 0 n 3 0 /two three 3 n 0 n 10 0 /three
3.2.1 Listing Tasks With proc #
Operation of the proc subcommand follows the same
model as the set subcommand. For example, to list
tasks in a cpuset, you need to use the -l/--list option
and specify the cpuset by name or, if the name exists multiple times in
the cpuset hierarchy, by path. For example:
tux >csetproc -l -s two cset: "two" cpuset of CPUSPEC(2) with 3 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- root 16141 4300 Soth bash root 16171 16141 Soth bash root 16703 16171 Roth python ./cset proc -l two
This output shows us that the cpuset called two has CPU2 only attached
to it and is running three tasks: two shells and the
python command to list it. Note that cpusets are
inherited so that if a process is contained in a cpuset, then any
children it spawns also run within that set. In this case, the
python command to list set two was
run from a shell already running in set two. This can
be seen by the PPID (parent process ID) of the python
command matching the PID of the shell.
Additionally, the SPPr field needs explanation. SPPr
stands for State, Policy and Priority. You can see
that the initial two tasks are stopped and running in timeshare
priority, marked as oth (for
other). The last task is marked as running,
R and at timeshare priority,
oth. If any of these tasks would have been at real
time priority, the policy would be shown as f
for FIFO or r for round robin. The priority would
be a number from 1 to 99. See below for an example.
tux >csetproc -l -s root | head -7 cset: "root" cpuset of CPUSPEC(0-3) with 309 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- root 1 0 Soth init [5] root 2 0 Soth [kthreadd] root 3 2 Sf99 [migration/0] root 4 2 Sf99 [posix_cpu_timer]
This output shows the first few tasks in the root
cpuset. Note that both init and
[kthread] are running at timeshare; however, the
[migration/0] and
[posix_cpu_timer] kernel threads are running at
real-time policy of FIFO and priority of 99.
Incidentally, this output is from a system running the real-time Linux
kernel which runs some kernel threads at real-time priorities. And
finally, note that you can use cset as any other
Linux tool and include it in pipelines as in the example above.
Taking a peek into the third cpuset called three, we
see:
tux >csetproc -l -s three cset: "three" cpuset of CPUSPEC(3) with 10 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- alext 16165 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16169 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16170 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16237 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16491 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16492 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16493 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 17243 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 17244 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 17265 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -...
This output shows that a lot of beagled tasks are
running in this cpuset and it also shows an ellipsis
(…) at the end of their listings. If you see this
ellipsis, that means that the command was too long to fit onto an 80
character screen. To see the entire command line, use the
-v/--verbose flag:
tux >csetproc -l -s three -v | head -4 cset: "three" cpuset of CPUSPEC(3) with 10 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- alext 16165 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg --autostarted --indexing-delay 300
3.2.2 Execing Tasks with proc #
To exec a task into a cpuset, the proc subcommand
needs to be employed with the -e/--exec option. Let’s
exec a shell into the cpuset named two in our set.
First we check to see what is running that set:
tux >csetproc -l -s two cset: "two" cpuset of CPUSPEC(2) with 0 tasks runningtux >csetproc -s two -e bash cset: --> last message, executed args into cpuset "/two", new pid is: 20955tux >csetproc -l -s two cset: "two" cpuset of CPUSPEC(2) with 2 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- root 20955 19253 Soth bash root 20981 20955 Roth python ./cset proc -l two
You can see that initially, two had nothing running
in it. After the completion of the second command, we list
two again and see that there are two tasks running:
the shell which we execed and the python cset command
that is listing the cpuset. The reason for the second task is that the
cpuset property of a running task is inherited by all its children.
Since we executed the listing command from the new shell which was bound
to cpuset two, the resulting process for the listing is also bound to
cpuset two. Let’s test that by running a new
shell with no prefixed cset command.
tux >bashtux >csetproc -l -s two cset: "two" cpuset of CPUSPEC(2) with 3 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- root 20955 19253 Soth bash root 21118 20955 Soth bash root 21147 21118 Roth python ./cset proc -l two
Here again we see that the second shell, PID 21118,
has a parent PID of 20955 which is the first shell.
Both shells, and the listing command, are running in the two cpuset.
cset follows the tradition of separating the tool
options from the command to be execed options with a double dash
(--). This is not shown in this simple example, but
if the command you want to exec also takes options, separate them with
the double dash as follows:
tux >csetproc -s myset -e mycommand -- -v
The -v will be passed to
mycommand, and not to cset.
Execing a shell into a cpuset is a useful way to experiment with running tasks in that cpuset since all children of the shell will also run in the same cpuset. Finally, if you misspell the command to be execed, the result may be puzzling. For example:
tux >csetproc -s two -e blah-blah cset: --> last message, executed args into cpuset "/two", new pid is: 21655 cset: **> [Errno 2] No such file or directory
The result is no new process even though a new PID is output. The reason
for the message is of course that the cset process
forked in preparation for exec, but the command
blah-blah was not found to execute it.
3.2.3 Moving Tasks with proc #
Although the ability to exec a task into a cpuset is fundamental, you
will most likely be moving tasks between cpusets more often. Moving
tasks is accomplished with the -m/--move and
-p/--pid options to the proc
subcommand of cset. The move option
tells the proc subcommand that a task move is
requested. The -p/--pid option takes an argument called
a PIDSPEC (PID Specification). The PIDSPEC defines which tasks get
operated on.
The PIDSPEC can be a single process ID, a list of process IDs separated by commas, and a list of process ID ranges also separated by commas. For example:
--pid1234This PIDSPEC argument specifies that PID
1234will be moved.--pid1234,42,1934,15000,15001,15002This PIDSPEC argument specifies that only listed tasks will be moved.
-p5000,5100,6010-7000,9232This PIDSPEC argument specifies that tasks
5000,5100and9232will be moved along with any existing task with PID in the range6010through7000inclusive.
A range in a PIDSPEC does not need to have running tasks for every number in that range. In fact, it is not even an error if there are no tasks running in that range; none will be moved in that case. The range simply specifies to act on any tasks that have a PID or TID that is within that range.
In the following example, we move the current shell into the cpuset
named two with a range PIDSPEC and back out to the
root cpuset with the Bash variable for the current
PID.
tux >csetproc -l -s two cset: "two" cpuset of CPUSPEC(2) with 0 tasks runningtux >echo$$ 19253tux >csetproc -m -p 19250-19260 -t two cset: moving following pidspec: 19253 cset: moving 1 userspace tasks to /two cset: donetux >csetproc -l -s two cset: "two" cpuset of CPUSPEC(2) with 2 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- root 19253 16447 Roth bash root 29456 19253 Roth python ./cset proc -l -s twotux >csetproc -m -p $$ -t root cset: moving following pidspec: 19253 cset: moving 1 userspace tasks to / cset: donetux >csetproc -l -s two cset: "two" cpuset of CPUSPEC(2) with 0 tasks running
Use of the appropriate PIDSPEC can thus be handy to move tasks and
groups of tasks. Additionally, there is one more option that can help
with multi-threaded processes, and that is the
--threads flag. If this flag is used together with the
proc move command with a PIDSPEC and if any of the
task IDs in the PIDSPEC belongs to a thread in a process container, then
all the sibling threads in that process container
will also get moved. This flag provides an easy mechanism to move all
threads of a process by simply specifying one thread in that process. In
the following example, we move all the threads running in cpuset
three to cpuset two by using the
--threads flag.
tux >csetset two three cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- two 2 n 0 n 0 0 /two three 3 n 0 n 10 0 /threetux >csetproc -l -s three cset: "three" cpuset of CPUSPEC(3) with 10 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- alext 16165 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16169 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16170 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16237 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16491 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16492 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16493 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 17243 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 17244 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 27133 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -...tux >csetproc -m -p 16165 --threads -t two cset: moving following pidspec: 16491,16493,16492,16170,16165,16169,27133,17244,17243,16237 cset: moving 10 userspace tasks to /two [==================================================]% cset: donetux >csetset two three cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- two 2 n 0 n 10 0 /two three 3 n 0 n 0 0 /three
3.2.3.1 Moving All Tasks From One Cpuset to Another #
There is a special case for moving all tasks currently running in one
cpuset to another. This can be a common use case, and when you need to
do it, specifying a PIDSPEC with -p is not necessary
so long as you use the -f/--fromset
and the -t/--toset options.
In the following example, we move all 10 beagled
threads back to cpuset three with this method.
tux >csetproc -l two three cset: "two" cpuset of CPUSPEC(2) with 10 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- alext 16165 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -… alext 16169 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16170 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16237 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16491 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16492 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 16493 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 17243 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 17244 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... alext 27133 1 Soth beagled /usr/lib64/beagle/BeagleDaemon.exe --bg -... cset: "three" cpuset of CPUSPEC(3) with 0 tasks runningtux >csetproc -m -f two -t three cset: moving all tasks from two to /three cset: moving 10 userspace tasks to /three [==================================================]% cset: donetux >csetset two three cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- two 2 n 0 n 0 0 /two three 3 n 0 n 10 0 /three
3.2.3.2 Moving Kernel Threads With proc #
Kernel threads are special and cset detects tasks
that are kernel threads and will refuse to move them unless you also
add a -k/--kthread option to your
proc move command. Even if you include
-k, cset will still refuse to move
the kernel thread if they are bound to specific CPUs. The reason for
this is system protection.
Several kernel threads, especially on the real-time Linux kernel,
are bound to specific CPUs and depend on per-CPU kernel variables. If
you move these threads to a different CPU than what they are bound to,
you risk at best that the system will become horribly slow, and at
worst a system hang. If you must move those threads (after all,
cset needs to give the knowledgeable user access to
the keys), then you also need to use the --force
option.
--force With Care
Overriding a task move command with --force can have
dire consequences for the system. Be sure of the command before you
force it.
In the following example, we move all unbound kernel threads running in
the root cpuset to the cpuset named two by using the
-k option.
tux >csetproc -k -f root -t two cset: moving all kernel threads from / to /two cset: moving 70 kernel threads to: /two cset: --> not moving 76 threads (not unbound, use --force) [==================================================]% cset: done
You will note that we used the fromset→toset facility of the
proc subcommand and we only specified the
-k option (not the -m option). This
has the effect of moving all kernel threads only.
Note that only 70 actual kernel threads were moved and 76 were not. The
reason that 76 kernel threads were not moved was because they are bound
to specific CPUs. Now, let’s move those kernel threads back to
root.
tux >csetproc -k -f two -t root cset: moving all kernel threads from /two to / cset: ** no task matched move criteria cset: **> kernel tasks are bound, use --force if oktux >csetset -l -s two cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- two 2 n 0 n 70 0 /two
cset refused to move the kernel threads back to
root because it says that they are
“bound”. Let’s check this with the
taskset command.
tux >csetproc -l -s two | head -5 cset: "two" cpuset of CPUSPEC(2) with 70 tasks running USER PID PPID SPPr TASK NAME -------- ----- ----- ---- --------- root 2 0 Soth [kthreadd] root 55 2 Soth [khelper]tux >taskset-p 2 pid 2's current affinity mask: 4tux >csetset -l -s two cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- two 2 n 0 n 70 0 /two
Of course, since the cpuset named two only has CPU2
assigned to it, once we moved the unbound kernel threads from
root to two, their affinity masks
got automatically changed to only use CPU2. This is evident from the
taskset output which is a hex value. To really move
these threads back to root, we need to force the move as follows.
tux >csetproc -k -f two -t root --force cset: moving all kernel threads from /two to / cset: moving 70 kernel threads to: / [==================================================]% cset: done
3.2.4 Destroying Tasks #
There actually is no cset subcommand or option to
destroy tasks—it’s not really needed. Tasks exist and are accessible
on the system as normal, even if they happen to be running in one cpuset
or another. To destroy tasks, use the usual
Ctrl–C
method or by using the kill(1) command.
3.3 Implementing “Shielding” With set and proc #
With the preceding material on the set and
proc subcommands, we now have the background to
implement the basic shielding model, like the shield subcommand.
One may pose the question why we want to do this, especially since
shield already does it? The answer is that sometimes
one needs more functionality than shield need to
implement one’s shielding strategy. In those cases you need to first
stop using shield since that subcommand will interfere
with the further application of set and
proc. However, you will still need to implement the
functionality of shield to implement
successful shielding.
Remember from the above sections describing shield,
that shielding has at minimum three cpusets: root,
which is always present and contains all CPUs; system
which is the non-shielded set of CPUs and runs
unimportant system tasks; and user, which is the
shielded set of CPUs and runs your important tasks.
Remember also that shield moves all movable tasks into
system and, optionally, moves unbound kernel threads
into system as well.
You start first by creating the system and
user cpusets as follows. Let's assume that the machine
is a four-CPU machine without NUMA memory features. The system cpuset
should hold only CPU0 while the user cpuset should hold the rest of the
CPUs.
tux >csetset -c 0 -s system cset: --> created cpuset "system"tux >csetset -c 1-3 -s user cset: --> created cpuset "user"tux >csetset -l cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 333 2 / user 1-3 n 0 n 0 0 /user system 0 n 0 n 0 0 /system
Now, we need to move all running user processes into the
system cpuset.
tux >csetproc -m -f root -t system cset: moving all tasks from root to /system cset: moving 188 userspace tasks to /system [==================================================]% cset: donetux >csetset -l cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 146 2 / user 1-3 n 0 n 0 0 /user system 0 n 0 n 187 0 /system
We now have the basic shielding setup. Since all user space tasks are
running in system, anything that is spawned from them
will also run in system. The user
cpuset has nothing running in it unless you put tasks there with the
proc subcommand as described above. If you also want
to move movable kernel threads from root to
system (to achieve a form of “interrupt
shielding” on a real time Linux kernel, for example), you would
execute the following command as well:
tux >csetproc -k -f root -t system cset: moving all kernel threads from / to /system cset: moving 70 kernel threads to: /system cset: --> not moving 76 threads (not unbound, use --force) [==================================================]% cset: donetux >csetset -l cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 76 2 / user 1-3 n 0 n 0 0 /user system 0 n 0 n 257 0 /system
At this point, you have achieved the simple shielding model that the
shield subcommand provides. You can now add other
cpuset definitions to expand your shielding strategy beyond that simple
model.
3.4 Implementing Hierarchy With set and proc #
One popular extended shielding model is based on hierarchical cpusets, each with diminishing numbers of CPUs. This model is used to create priority cpusets that allow assignment of CPU resources to tasks based on some arbitrary priority definition. The idea is that a higher priority task will get access to more CPU resources than a lower priority task.
The example provided here once again assumes a machine with four CPUs and no NUMA memory features. This base serves to illustrate the point well; however, note that if your machine has (many) more CPUs, then strategies such as this and others get more interesting.
We define a shielding setup as in the previous section where we have a
system cpuset with only CPU0 that takes care of
“unimportant” system tasks. You will usually require this
type of cpuset since it forms the basis of shielding. We modify the
strategy to not use a user cpuset; instead we create
several new cpusets each holding one more CPU than the other. These
cpusets will be called prio_low with one CPU,
prio_med with two CPUs, prio_high
with three CPUs, and prio_all with all CPUs.
You may ask, why create a prio_all with all CPUs when
that is substantially the definition of the root
cpuset? The answer is that it is best to keep a separation between the
root cpuset and everything else, even if a particular
cpuset duplicates root exactly. Usually, automation
is build on top of a cpuset strategy. In these cases, it is best to
avoid using invariant names of cpusets, such as root
for example, in this automation.
All of these prio_* cpusets can be created under root,
in a flat way; however, it is advantageous to create them as a hierarchy.
The reasoning for this is twofold: first, if a cpuset is destroyed, all
its tasks are moved to its parent; second, one can use exclusive CPUs in
a hierarchy.
If a cpuset has CPUs that are exclusive to it, then other cpusets may not use those CPUs unless they are children of that cpuset. This has more relevance to machines with many CPUs and more complex strategies.
Now, we start with a clean slate and build the appropriate cpusets as follows.
tux >csetset -r cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 344 0 /tux >csetset -c 0-3 prio_all cset: --> created cpuset "prio_all"tux >csetset -c 1-3 /prio_all/prio_high cset: --> created cpuset "/prio_all/prio_high"tux >csetset -c 2-3 /prio_all/prio_high/prio_med cset: --> created cpuset "/prio_all/prio_high/prio_med"tux >csetset -c 3 /prio_all/prio_high/prio_med/prio_low cset: --> created cpuset "/prio_all/prio_high/prio_med/prio_low"tux >csetset -c 0 system cset: --> created cpuset "system"tux >csetset -l -r cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 344 2 / system 0 n 0 n 0 0 /system prio_all 0-3 n 0 n 0 1 /prio_all prio_high 1-3 n 0 n 0 1 /prio_all/prio_high prio_med 2-3 n 0 n 0 1 /prio_all/prio_high/prio_med prio_low 3 n 0 n 0 0 /prio_all/pr...rio_med/prio_low
-r/--recurse Is Needed in This Case
The option -r/--recurse lists all the
sets in the last command above. If you execute that command without
-r/--recurse, prio_med and
prio_low cpusets would not appear.
The strategy is now implemented and we now move all user space tasks
and all movable kernel threads into the system
cpuset to activate the shield.
tux >csetproc -m -k -f root -t system cset: moving all tasks from root to /system cset: moving 198 userspace tasks to /system cset: moving 70 kernel threads to: /system cset: --> not moving 76 threads (not unbound, use --force) [==================================================]% cset: donetux >csetset -l -r cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 76 2 / system 0 n 0 n 268 0 /system prio_all 0-3 n 0 n 0 1 /prio_all prio_high 1-3 n 0 n 0 1 /prio_all/prio_high prio_med 2-3 n 0 n 0 1 /prio_all/prio_high/prio_med prio_low 3 n 0 n 0 0 /prio_all/pr...rio_med/prio_low
The shield is now active. Since the prio_* cpuset
names are unique, you can assign tasks to them either via their simple
name, or their full path (as described in
Section 3.2.2, “Execing Tasks with proc”).
You may have noted that there is an ellipsis in the path of the
prio_low cpuset in the listing above. This is done
to fit the output onto an 80 character screen. To see
the entire line, use the -v/--verbose
flag as follows:
tux >csetset -l -r -v cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0-3 y 0 y 76 2 / system 0 n 0 n 268 0 /system prio_all 0-3 n 0 n 0 1 /prio_all prio_high 1-3 n 0 n 0 1 /prio_all/prio_high prio_med 2-3 n 0 n 0 1 /prio_all/prio_high/prio_med prio_low 3 n 0 n 0 0 /prio_all/prio_high/prio_med/prio_low