[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>

[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>
Satoru Takeuchi · Linus Torvalds
1 parent fca4edb48b
Showing 1 changed file with 74 additions and 74 deletions Side-by-side Diff
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.
...	...	@@ -46,7 +46,7 @@
46	46	maxcpus=2 will only boot 2. You can choose to bring the
47	47	other cpus later online, read FAQ's for more info.
48	48
49		-additional_cpus*=n Use this to limit hotpluggable cpus. This option sets
	49	+additional_cpus=n (*) Use this to limit hotpluggable cpus. This option sets
50	50	cpu_possible_map = cpu_present_map + additional_cpus
51	51
52	52	(*) Option valid only for following architectures
53	53
54	54
...	...	@@ -101,15 +101,15 @@
101	101
102	102	Never use anything other than cpumask_t to represent bitmap of CPUs.
103	103
104		-#include <linux/cpumask.h>
	104	+ #include <linux/cpumask.h>
105	105
106		-for_each_possible_cpu - Iterate over cpu_possible_map
107		-for_each_online_cpu - Iterate over cpu_online_map
108		-for_each_present_cpu - Iterate over cpu_present_map
109		-for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.
	106	+ for_each_possible_cpu - Iterate over cpu_possible_map
	107	+ for_each_online_cpu - Iterate over cpu_online_map
	108	+ for_each_present_cpu - Iterate over cpu_present_map
	109	+ for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.
110	110
111		-#include <linux/cpu.h>
112		-lock_cpu_hotplug() and unlock_cpu_hotplug():
	111	+ #include <linux/cpu.h>
	112	+ lock_cpu_hotplug() and unlock_cpu_hotplug():
113	113
114	114	The above calls are used to inhibit cpu hotplug operations. While holding the
115	115	cpucontrol mutex, cpu_online_map will not change. If you merely need to avoid
...	...	@@ -120,7 +120,7 @@
120	120
121	121	CPU Hotplug - Frequently Asked Questions.
122	122
123		-Q: How to i enable my kernel to support CPU hotplug?
	123	+Q: How to enable my kernel to support CPU hotplug?
124	124	A: When doing make defconfig, Enable CPU hotplug support
125	125
126	126	"Processor type and Features" -> Support for Hotpluggable CPUs
127	127
128	128
129	129
130	130
131	131
...	...	@@ -141,39 +141,39 @@
141	141	Check if sysfs is mounted, using the "mount" command. You should notice
142	142	an entry as shown below in the output.
143	143
144		-....
145		-none on /sys type sysfs (rw)
146		-....
	144	+ ....
	145	+ none on /sys type sysfs (rw)
	146	+ ....
147	147
148		-if this is not mounted, do the following.
	148	+If this is not mounted, do the following.
149	149
150		-#mkdir /sysfs
151		-#mount -t sysfs sys /sys
	150	+ #mkdir /sysfs
	151	+ #mount -t sysfs sys /sys
152	152
153		-now you should see entries for all present cpu, the following is an example
	153	+Now you should see entries for all present cpu, the following is an example
154	154	in a 8-way system.
155	155
156		-#pwd
157		-#/sys/devices/system/cpu
158		-#ls -l
159		-total 0
160		-drwxr-xr-x 10 root root 0 Sep 19 07:44 .
161		-drwxr-xr-x 13 root root 0 Sep 19 07:45 ..
162		-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu0
163		-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu1
164		-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu2
165		-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu3
166		-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu4
167		-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu5
168		-drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu6
169		-drwxr-xr-x 3 root root 0 Sep 19 07:48 cpu7
	156	+ #pwd
	157	+ #/sys/devices/system/cpu
	158	+ #ls -l
	159	+ total 0
	160	+ drwxr-xr-x 10 root root 0 Sep 19 07:44 .
	161	+ drwxr-xr-x 13 root root 0 Sep 19 07:45 ..
	162	+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu0
	163	+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu1
	164	+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu2
	165	+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu3
	166	+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu4
	167	+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu5
	168	+ drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu6
	169	+ drwxr-xr-x 3 root root 0 Sep 19 07:48 cpu7
170	170
171	171	Under each directory you would find an "online" file which is the control
172	172	file to logically online/offline a processor.
173	173
174	174	Q: Does hot-add/hot-remove refer to physical add/remove of cpus?
175	175	A: The usage of hot-add/remove may not be very consistently used in the code.
176		-CONFIG_CPU_HOTPLUG enables logical online/offline capability in the kernel.
	176	+CONFIG_HOTPLUG_CPU enables logical online/offline capability in the kernel.
177	177	To support physical addition/removal, one would need some BIOS hooks and
178	178	the platform should have something like an attention button in PCI hotplug.
179	179	CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of CPUs.
180	180
181	181
182	182
183	183
...	...	@@ -181,17 +181,17 @@
181	181	Q: How do i logically offline a CPU?
182	182	A: Do the following.
183	183
184		-#echo 0 > /sys/devices/system/cpu/cpuX/online
	184	+ #echo 0 > /sys/devices/system/cpu/cpuX/online
185	185
186		-once the logical offline is successful, check
	186	+Once the logical offline is successful, check
187	187
188		-#cat /proc/interrupts
	188	+ #cat /proc/interrupts
189	189
190		-you should now not see the CPU that you removed. Also online file will report
	190	+You should now not see the CPU that you removed. Also online file will report
191	191	the state as 0 when a cpu if offline and 1 when its online.
192	192
193		-#To display the current cpu state.
194		-#cat /sys/devices/system/cpu/cpuX/online
	193	+ #To display the current cpu state.
	194	+ #cat /sys/devices/system/cpu/cpuX/online
195	195
196	196	Q: Why cant i remove CPU0 on some systems?
197	197	A: Some architectures may have some special dependency on a certain CPU.
...	...	@@ -234,8 +234,8 @@
234	234	departure, how to i arrange for proper notification?
235	235	A: This is what you would need in your kernel code to receive notifications.
236	236
237		- #include <linux/cpu.h>
238		- static int __cpuinit foobar_cpu_callback(struct notifier_block *nfb,
	237	+ #include <linux/cpu.h>
	238	+ static int __cpuinit foobar_cpu_callback(struct notifier_block *nfb,
239	239	unsigned long action, void *hcpu)
240	240	{
241	241	unsigned int cpu = (unsigned long)hcpu;
242	242
...	...	@@ -279,10 +279,10 @@
279	279	A: Yes, CPU notifiers are called only when new CPUs are on-lined or offlined.
280	280	If you need to perform some action for each cpu already in the system, then
281	281
282		- for_each_online_cpu(i) {
	282	+ for_each_online_cpu(i) {
283	283	foobar_cpu_callback(&foobar_cpu_notifier, CPU_UP_PREPARE, i);
284		- foobar_cpu_callback(&foobar-cpu_notifier, CPU_ONLINE, i);
285		- }
	284	+ foobar_cpu_callback(&foobar_cpu_notifier, CPU_ONLINE, i);
	285	+ }
286	286
287	287	Q: If i would like to develop cpu hotplug support for a new architecture,
288	288	what do i need at a minimum?
289	289
290	290
291	291
292	292
...	...	@@ -307,38 +307,38 @@
307	307	work specific to this cpu is in progress.
308	308	A: First switch the current thread context to preferred cpu
309	309
310		- int my_func_on_cpu(int cpu)
311		- {
312		- cpumask_t saved_mask, new_mask = CPU_MASK_NONE;
313		- int curr_cpu, err = 0;
	310	+ int my_func_on_cpu(int cpu)
	311	+ {
	312	+ cpumask_t saved_mask, new_mask = CPU_MASK_NONE;
	313	+ int curr_cpu, err = 0;
314	314
315		- saved_mask = current->cpus_allowed;
316		- cpu_set(cpu, new_mask);
317		- err = set_cpus_allowed(current, new_mask);
	315	+ saved_mask = current->cpus_allowed;
	316	+ cpu_set(cpu, new_mask);
	317	+ err = set_cpus_allowed(current, new_mask);
318	318
319		- if (err)
320		- return err;
	319	+ if (err)
	320	+ return err;
321	321
322		- /*
323		- * If we got scheduled out just after the return from
324		- * set_cpus_allowed() before running the work, this ensures
325		- * we stay locked.
326		- */
327		- curr_cpu = get_cpu();
	322	+ /*
	323	+ * If we got scheduled out just after the return from
	324	+ * set_cpus_allowed() before running the work, this ensures
	325	+ * we stay locked.
	326	+ */
	327	+ curr_cpu = get_cpu();
328	328
329		- if (curr_cpu != cpu) {
330		- err = -EAGAIN;
331		- goto ret;
332		- } else {
333		- /*
334		- * Do work : But cant sleep, since get_cpu() disables preempt
335		- */
336		- }
337		- ret:
338		- put_cpu();
339		- set_cpus_allowed(current, saved_mask);
340		- return err;
341		- }
	329	+ if (curr_cpu != cpu) {
	330	+ err = -EAGAIN;
	331	+ goto ret;
	332	+ } else {
	333	+ /*
	334	+ * Do work : But cant sleep, since get_cpu() disables preempt
	335	+ */
	336	+ }
	337	+ ret:
	338	+ put_cpu();
	339	+ set_cpus_allowed(current, saved_mask);
	340	+ return err;
	341	+ }
342	342
343	343
344	344	Q: How do we determine how many CPUs are available for hotplug.