Joel Schopp <jschopp@austin.ibm.com>
ia64/x86_64:
Ashok Raj <ashok.raj@intel.com>
+ s390:
+ Heiko Carstens <heiko.carstens@de.ibm.com>
Authors: Ashok Raj <ashok.raj@intel.com>
Lots of feedback: Nathan Lynch <nathanl@austin.ibm.com>,
other cpus later online, read FAQ's for more info.
additional_cpus*=n Use this to limit hotpluggable cpus. This option sets
- cpu_possible_map = cpu_present_map + additional_cpus
+ cpu_possible_map = cpu_present_map + additional_cpus
(*) Option valid only for following architectures
-- x86_64, ia64
+- x86_64, ia64, s390
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
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.
+ 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
-----------------
You really dont need to manipulate any of the system cpu maps. They should
be read-only for most use. When setting up per-cpu resources almost always use
-cpu_possible_map/for_each_cpu() to iterate.
+cpu_possible_map/for_each_possible_cpu() to iterate.
Never use anything other than cpumask_t to represent bitmap of CPUs.
#include <linux/cpumask.h>
-for_each_cpu - Iterate over cpu_possible_map
+for_each_possible_cpu - Iterate over cpu_possible_map
for_each_online_cpu - Iterate over cpu_online_map
for_each_present_cpu - Iterate over cpu_present_map
for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.
return NOTIFY_OK;
}
- static struct notifier_block foobar_cpu_notifer =
+ static struct notifier_block __cpuinitdata foobar_cpu_notifer =
{
.notifier_call = foobar_cpu_callback,
};
+You need to call register_cpu_notifier() from your init function.
+Init functions could be of two types:
+1. early init (init function called when only the boot processor is online).
+2. late init (init function called _after_ all the CPUs are online).
-In your init function,
+For the first case, you should add the following to your init function
register_cpu_notifier(&foobar_cpu_notifier);
+For the second case, you should add the following to your init function
+
+ register_hotcpu_notifier(&foobar_cpu_notifier);
+
You can fail PREPARE notifiers if something doesn't work to prepare resources.
This will stop the activity and send a following CANCELED event back.