Using CPU hotplug
=================
+
The kernel option *CONFIG_HOTPLUG_CPU* needs to be enabled. It is currently
available on multiple architectures including ARM, MIPS, PowerPC and X86. The
-configuration is done via the sysfs interface: ::
+configuration is done via the sysfs interface::
$ ls -lh /sys/devices/system/cpu
total 0
The files *offline*, *online*, *possible*, *present* represent the CPU masks.
Each CPU folder contains an *online* file which controls the logical on (1) and
-off (0) state. To logically shutdown CPU4: ::
+off (0) state. To logically shutdown CPU4::
$ echo 0 > /sys/devices/system/cpu/cpu4/online
smpboot: CPU 4 is now offline
Once the CPU is shutdown, it will be removed from */proc/interrupts*,
*/proc/cpuinfo* and should also not be shown visible by the *top* command. To
-bring CPU4 back online: ::
+bring CPU4 back online::
$ echo 1 > /sys/devices/system/cpu/cpu4/online
smpboot: Booting Node 0 Processor 4 APIC 0x1
The offline case
----------------
+
Once a CPU has been logically shutdown the teardown callbacks of registered
hotplug states will be invoked, starting with ``CPUHP_ONLINE`` and terminating
at state ``CPUHP_OFFLINE``. This includes:
Using the hotplug API
---------------------
+
It is possible to receive notifications once a CPU is offline or onlined. This
might be important to certain drivers which need to perform some kind of setup
-or clean up functions based on the number of available CPUs: ::
+or clean up functions based on the number of available CPUs::
#include <linux/cpuhotplug.h>
Multiple instances
~~~~~~~~~~~~~~~~~~
+
If a driver has multiple instances and each instance needs to perform the
callback independently then it is likely that a ''multi-state'' should be used.
-First a multi-state state needs to be registered: ::
+First a multi-state state needs to be registered::
ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "X/Y:online,
Y_online, Y_prepare_down);
The ``cpuhp_setup_state_multi()`` behaves similar to ``cpuhp_setup_state()``
except it prepares the callbacks for a multi state and does not invoke
the callbacks. This is a one time setup.
-Once a new instance is allocated, you need to register this new instance: ::
+Once a new instance is allocated, you need to register this new instance::
ret = cpuhp_state_add_instance(Y_hp_online, &d->node);
(*Y_online*) on all online CPUs. The *node* element is a ``struct
hlist_node`` member of your per-instance data structure.
-On removal of the instance: ::
+On removal of the instance::
+
cpuhp_state_remove_instance(Y_hp_online, &d->node)
should be invoked which will invoke the teardown callback on all online
Manual setup
~~~~~~~~~~~~
+
Usually it is handy to invoke setup and teardown callbacks on registration or
removal of a state because usually the operation needs to performed once a CPU
goes online (offline) and during initial setup (shutdown) of the driver. However
The ordering of the events
--------------------------
+
The hotplug states are defined in ``include/linux/cpuhotplug.h``:
* The states *CPUHP_OFFLINE* … *CPUHP_AP_OFFLINE* are invoked before the
Testing of hotplug states
=========================
+
One way to verify whether a custom state is working as expected or not is to
shutdown a CPU and then put it online again. It is also possible to put the CPU
to certain state (for instance *CPUHP_AP_ONLINE*) and then go back to
*CPUHP_ONLINE*. This would simulate an error one state after *CPUHP_AP_ONLINE*
which would lead to rollback to the online state.
-All registered states are enumerated in ``/sys/devices/system/cpu/hotplug/states``: ::
+All registered states are enumerated in ``/sys/devices/system/cpu/hotplug/states`` ::
$ tail /sys/devices/system/cpu/hotplug/states
138: mm/vmscan:online
168: sched:active
169: online
-To rollback CPU4 to ``lib/percpu_cnt:online`` and back online just issue: ::
+To rollback CPU4 to ``lib/percpu_cnt:online`` and back online just issue::
$ cat /sys/devices/system/cpu/cpu4/hotplug/state
169
$ cat /sys/devices/system/cpu/cpu4/hotplug/state
140
-It is important to note that the teardown callbac of state 140 have been
-invoked. And now get back online: ::
+It is important to note that the teardown callback of state 140 have been
+invoked. And now get back online::
$ echo 169 > /sys/devices/system/cpu/cpu4/hotplug/target
$ cat /sys/devices/system/cpu/cpu4/hotplug/state
169
-With trace events enabled, the individual steps are visible, too: ::
+With trace events enabled, the individual steps are visible, too::
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
Architecture's requirements
===========================
+
The following functions and configurations are required:
``CONFIG_HOTPLUG_CPU``
User Space Notification
=======================
-After CPU successfully onlined or offline udev events are sent. A udev rule like: ::
+
+After CPU successfully onlined or offline udev events are sent. A udev rule like::
SUBSYSTEM=="cpu", DRIVERS=="processor", DEVPATH=="/devices/system/cpu/*", RUN+="the_hotplug_receiver.sh"
-will receive all events. A script like: ::
+will receive all events. A script like::
#!/bin/sh
projects / linux-2.6-microblaze.git / blobdiff