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Commit ca926e80 authored by Satoru Takeuchi's avatar Satoru Takeuchi Committed by Linus Torvalds
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[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: default avatarSatoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent fca4edb4

Documentation/cpu-hotplug.txt

+74 −74
Original line number Diff line number Diff line
@@ -46,7 +46,7 @@ maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using 
             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
@@ -120,7 +120,7 @@ will work as long as stop_machine_run() is used to take a cpu down. 


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
@@ -145,12 +145,12 @@ an entry as shown below in the output. 
	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



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
@@ -173,7 +173,7 @@ 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.
@@ -183,11 +183,11 @@ A: Do the following. 


	#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



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.
@@ -281,7 +281,7 @@ A: Yes, CPU notifiers are called only when new CPUs are on-lined or offlined. 


	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,