Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394...

[sfrench/cifs-2.6.git] / Documentation / cpu-hotplug.txt

diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index cc60d29b954cd394ccd1eba1c27b06bfc049302d..ba0aacde94fba2472d33ba9da5764a2b8cc5f63e 100644 (file)
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -50,7 +50,7 @@ additional_cpus=n (*) Use this to limit hotpluggable cpus. This option sets
                        cpu_possible_map = cpu_present_map + additional_cpus
 
 (*) Option valid only for following architectures
-- x86_64, ia64, s390
+- x86_64, ia64
 
 ia64 and x86_64 use the number of disabled local apics in ACPI tables MADT
 to determine the number of potentially hot-pluggable cpus. The implementation
@@ -109,12 +109,13 @@ Never use anything other than cpumask_t to represent bitmap of CPUs.
        for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.
 
        #include <linux/cpu.h>
-       lock_cpu_hotplug() and unlock_cpu_hotplug():
+       get_online_cpus() and put_online_cpus():
 
-The above calls are used to inhibit cpu hotplug operations. While holding the
-cpucontrol mutex, cpu_online_map will not change. If you merely need to avoid
-cpus going away, you could also use preempt_disable() and preempt_enable()
-for those sections. Just remember the critical section cannot call any
+The above calls are used to inhibit cpu hotplug operations. While the
+cpu_hotplug.refcount is non zero, the cpu_online_map will not change.
+If you merely need to avoid cpus going away, you could also use
+preempt_disable() and preempt_enable() for those sections.
+Just remember the critical section cannot call any
 function that can sleep or schedule this process away. The preempt_disable()
 will work as long as stop_machine_run() is used to take a cpu down.
 
@@ -217,14 +218,19 @@ Q: What happens when a CPU is being logically offlined?
 A: The following happen, listed in no particular order :-)
 
 - A notification is sent to in-kernel registered modules by sending an event
-  CPU_DOWN_PREPARE
-- All process is migrated away from this outgoing CPU to a new CPU
+  CPU_DOWN_PREPARE or CPU_DOWN_PREPARE_FROZEN, depending on whether or not the
+  CPU is being offlined while tasks are frozen due to a suspend operation in
+  progress
+- All processes are migrated away from this outgoing CPU to new CPUs.
+  The new CPU is chosen from each process' current cpuset, which may be
+  a subset of all online CPUs.
 - All interrupts targeted to this CPU is migrated to a new CPU
 - timers/bottom half/task lets are also migrated to a new CPU
 - Once all services are migrated, kernel calls an arch specific routine
   __cpu_disable() to perform arch specific cleanup.
 - Once this is successful, an event for successful cleanup is sent by an event
-  CPU_DEAD.
+  CPU_DEAD (or CPU_DEAD_FROZEN if tasks are frozen due to a suspend while the
+  CPU is being offlined).
 
   "It is expected that each service cleans up when the CPU_DOWN_PREPARE
   notifier is called, when CPU_DEAD is called its expected there is nothing
@@ -242,9 +248,11 @@ A: This is what you would need in your kernel code to receive notifications.
 
                switch (action) {
                case CPU_ONLINE:
+               case CPU_ONLINE_FROZEN:
                        foobar_online_action(cpu);
                        break;
                case CPU_DEAD:
+               case CPU_DEAD_FROZEN:
                        foobar_dead_action(cpu);
                        break;
                }