diff options
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
| -rw-r--r-- | Documentation/cpu-hotplug.txt | 53 |
1 files changed, 49 insertions, 4 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index edd4b4df393..a0b005d2bd9 100644 --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -5,7 +5,7 @@ Rusty Russell <rusty@rustcorp.com.au> Srivatsa Vaddagiri <vatsa@in.ibm.com> i386: - Zwane Mwaikambo <zwane@arm.linux.org.uk> + Zwane Mwaikambo <zwanem@gmail.com> ppc64: Nathan Lynch <nathanl@austin.ibm.com> Joel Schopp <jschopp@austin.ibm.com> @@ -267,8 +267,8 @@ Q: If i have some kernel code that needs to be aware of CPU arrival and A: This is what you would need in your kernel code to receive notifications. #include <linux/cpu.h> - static int __cpuinit foobar_cpu_callback(struct notifier_block *nfb, - unsigned long action, void *hcpu) + static int foobar_cpu_callback(struct notifier_block *nfb, + unsigned long action, void *hcpu) { unsigned int cpu = (unsigned long)hcpu; @@ -285,7 +285,7 @@ A: This is what you would need in your kernel code to receive notifications. return NOTIFY_OK; } - static struct notifier_block __cpuinitdata foobar_cpu_notifer = + static struct notifier_block foobar_cpu_notifier = { .notifier_call = foobar_cpu_callback, }; @@ -312,12 +312,57 @@ things will happen if a notifier in path sent a BAD notify code. Q: I don't see my action being called for all CPUs already up and running? A: Yes, CPU notifiers are called only when new CPUs are on-lined or offlined. If you need to perform some action for each cpu already in the system, then + do this: for_each_online_cpu(i) { foobar_cpu_callback(&foobar_cpu_notifier, CPU_UP_PREPARE, i); foobar_cpu_callback(&foobar_cpu_notifier, CPU_ONLINE, i); } + However, if you want to register a hotplug callback, as well as perform + some initialization for CPUs that are already online, then do this: + + Version 1: (Correct) + --------- + + cpu_notifier_register_begin(); + + for_each_online_cpu(i) { + foobar_cpu_callback(&foobar_cpu_notifier, + CPU_UP_PREPARE, i); + foobar_cpu_callback(&foobar_cpu_notifier, + CPU_ONLINE, i); + } + + /* Note the use of the double underscored version of the API */ + __register_cpu_notifier(&foobar_cpu_notifier); + + cpu_notifier_register_done(); + + Note that the following code is *NOT* the right way to achieve this, + because it is prone to an ABBA deadlock between the cpu_add_remove_lock + and the cpu_hotplug.lock. + + Version 2: (Wrong!) + --------- + + get_online_cpus(); + + for_each_online_cpu(i) { + foobar_cpu_callback(&foobar_cpu_notifier, + CPU_UP_PREPARE, i); + foobar_cpu_callback(&foobar_cpu_notifier, + CPU_ONLINE, i); + } + + register_cpu_notifier(&foobar_cpu_notifier); + + put_online_cpus(); + + So always use the first version shown above when you want to register + callbacks as well as initialize the already online CPUs. + + Q: If i would like to develop cpu hotplug support for a new architecture, what do i need at a minimum? A: The following are what is required for CPU hotplug infrastructure to work |