[PATCH] doc: fixing cpu-hotplug documentation
Fixing cpu-hotplug documentation as follows:
- moving confusing asterisk on additional_cpus descrition
- fixing some typos
- unifying indentation for source code and command line example
Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index bc107cb..4868c34 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -46,7 +46,7 @@
maxcpus=2 will only boot 2. You can choose to bring the
other cpus later online, read FAQ's for more info.
-additional_cpus*=n Use this to limit hotpluggable cpus. This option sets
+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
@@ -101,15 +101,15 @@
Never use anything other than cpumask_t to represent bitmap of CPUs.
-#include <linux/cpumask.h>
+ #include <linux/cpumask.h>
-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.
+ 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.
-#include <linux/cpu.h>
-lock_cpu_hotplug() and unlock_cpu_hotplug():
+ #include <linux/cpu.h>
+ lock_cpu_hotplug() and unlock_cpu_hotplug():
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
@@ -120,7 +120,7 @@
CPU Hotplug - Frequently Asked Questions.
-Q: How to i enable my kernel to support CPU hotplug?
+Q: How to enable my kernel to support CPU hotplug?
A: When doing make defconfig, Enable CPU hotplug support
"Processor type and Features" -> Support for Hotpluggable CPUs
@@ -141,39 +141,39 @@
Check if sysfs is mounted, using the "mount" command. You should notice
an entry as shown below in the output.
-....
-none on /sys type sysfs (rw)
-....
+ ....
+ none on /sys type sysfs (rw)
+ ....
-if this is not mounted, do the following.
+If this is not mounted, do the following.
-#mkdir /sysfs
-#mount -t sysfs sys /sys
+ #mkdir /sysfs
+ #mount -t sysfs sys /sys
-now you should see entries for all present cpu, the following is an example
+Now you should see entries for all present cpu, the following is an example
in a 8-way system.
-#pwd
-#/sys/devices/system/cpu
-#ls -l
-total 0
-drwxr-xr-x 10 root root 0 Sep 19 07:44 .
-drwxr-xr-x 13 root root 0 Sep 19 07:45 ..
-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu0
-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu1
-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu2
-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu3
-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu4
-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu5
-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu6
-drwxr-xr-x 3 root root 0 Sep 19 07:48 cpu7
+ #pwd
+ #/sys/devices/system/cpu
+ #ls -l
+ total 0
+ drwxr-xr-x 10 root root 0 Sep 19 07:44 .
+ drwxr-xr-x 13 root root 0 Sep 19 07:45 ..
+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu0
+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu1
+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu2
+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu3
+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu4
+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu5
+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu6
+ drwxr-xr-x 3 root root 0 Sep 19 07:48 cpu7
Under each directory you would find an "online" file which is the control
file to logically online/offline a processor.
Q: Does hot-add/hot-remove refer to physical add/remove of cpus?
A: The usage of hot-add/remove may not be very consistently used in the code.
-CONFIG_CPU_HOTPLUG enables logical online/offline capability in the kernel.
+CONFIG_HOTPLUG_CPU enables logical online/offline capability in the kernel.
To support physical addition/removal, one would need some BIOS hooks and
the platform should have something like an attention button in PCI hotplug.
CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of CPUs.
@@ -181,17 +181,17 @@
Q: How do i logically offline a CPU?
A: Do the following.
-#echo 0 > /sys/devices/system/cpu/cpuX/online
+ #echo 0 > /sys/devices/system/cpu/cpuX/online
-once the logical offline is successful, check
+Once the logical offline is successful, check
-#cat /proc/interrupts
+ #cat /proc/interrupts
-you should now not see the CPU that you removed. Also online file will report
+You should now not see the CPU that you removed. Also online file will report
the state as 0 when a cpu if offline and 1 when its online.
-#To display the current cpu state.
-#cat /sys/devices/system/cpu/cpuX/online
+ #To display the current cpu state.
+ #cat /sys/devices/system/cpu/cpuX/online
Q: Why cant i remove CPU0 on some systems?
A: Some architectures may have some special dependency on a certain CPU.
@@ -234,8 +234,8 @@
departure, how to i arrange for proper notification?
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,
+ #include <linux/cpu.h>
+ static int __cpuinit foobar_cpu_callback(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
unsigned int cpu = (unsigned long)hcpu;
@@ -279,10 +279,10 @@
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
- for_each_online_cpu(i) {
+ for_each_online_cpu(i) {
foobar_cpu_callback(&foobar_cpu_notifier, CPU_UP_PREPARE, i);
- foobar_cpu_callback(&foobar-cpu_notifier, CPU_ONLINE, i);
- }
+ foobar_cpu_callback(&foobar_cpu_notifier, CPU_ONLINE, i);
+ }
Q: If i would like to develop cpu hotplug support for a new architecture,
what do i need at a minimum?
@@ -307,38 +307,38 @@
work specific to this cpu is in progress.
A: First switch the current thread context to preferred cpu
- int my_func_on_cpu(int cpu)
- {
- cpumask_t saved_mask, new_mask = CPU_MASK_NONE;
- int curr_cpu, err = 0;
+ int my_func_on_cpu(int cpu)
+ {
+ cpumask_t saved_mask, new_mask = CPU_MASK_NONE;
+ int curr_cpu, err = 0;
- saved_mask = current->cpus_allowed;
- cpu_set(cpu, new_mask);
- err = set_cpus_allowed(current, new_mask);
+ saved_mask = current->cpus_allowed;
+ cpu_set(cpu, new_mask);
+ err = set_cpus_allowed(current, new_mask);
- if (err)
- return err;
+ if (err)
+ return err;
- /*
- * If we got scheduled out just after the return from
- * set_cpus_allowed() before running the work, this ensures
- * we stay locked.
- */
- curr_cpu = get_cpu();
+ /*
+ * If we got scheduled out just after the return from
+ * set_cpus_allowed() before running the work, this ensures
+ * we stay locked.
+ */
+ curr_cpu = get_cpu();
- if (curr_cpu != cpu) {
- err = -EAGAIN;
- goto ret;
- } else {
- /*
- * Do work : But cant sleep, since get_cpu() disables preempt
- */
- }
- ret:
- put_cpu();
- set_cpus_allowed(current, saved_mask);
- return err;
- }
+ if (curr_cpu != cpu) {
+ err = -EAGAIN;
+ goto ret;
+ } else {
+ /*
+ * Do work : But cant sleep, since get_cpu() disables preempt
+ */
+ }
+ ret:
+ put_cpu();
+ set_cpus_allowed(current, saved_mask);
+ return err;
+ }
Q: How do we determine how many CPUs are available for hotplug.
