cpu_possible_map = cpu_present_map + additional_cpus
(*) Option valid only for following architectures
-- x86_64, ia64, s390
+- 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
-should only rely on this to count the #of cpus, but *MUST* not rely on the
-apicid values in those tables for disabled apics. In the event BIOS doesnt
-mark such hot-pluggable cpus as disabled entries, one could use this
-parameter "additional_cpus=x" to represent those cpus in the cpu_possible_map.
+ia64 uses the number of disabled local apics in ACPI tables MADT to
+determine the number of potentially hot-pluggable cpus. The implementation
+should only rely on this to count the # of cpus, but *MUST* not rely
+on the apicid values in those tables for disabled apics. In the event
+BIOS doesn't mark such hot-pluggable cpus as disabled entries, one could
+use this parameter "additional_cpus=x" to represent those cpus in the
+cpu_possible_map.
-s390 uses the number of cpus it detects at IPL time to also the number of bits
-in cpu_possible_map. If it is desired to add additional cpus at a later time
-the number should be specified using this option or the possible_cpus option.
-
-possible_cpus=n [s390 only] use this to set hotpluggable cpus.
+possible_cpus=n [s390,x86_64] use this to set hotpluggable cpus.
This option sets possible_cpus bits in
cpu_possible_map. Thus keeping the numbers of bits set
constant even if the machine gets rebooted.
- This option overrides additional_cpus.
CPU maps and such
-----------------
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.
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
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;
}
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff