diff options
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
| -rw-r--r-- | Documentation/cpu-hotplug.txt | 148 |
1 files changed, 74 insertions, 74 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index bc107cb157a8..4868c34f7509 100644 --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -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 @@ -101,15 +101,15 @@ 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> + #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 @@ 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 @@ -141,39 +141,39 @@ A: You should now notice an entry in sysfs. 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 @@ CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of CPUs. 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 @@ Q: If i have some kernel code that needs to be aware of CPU arrival and 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 @@ 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 - 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 @@ Q: I need to ensure that a particular cpu is not removed when there is some 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; - - saved_mask = current->cpus_allowed; - cpu_set(cpu, new_mask); - err = set_cpus_allowed(current, new_mask); - - 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 (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; - } + 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); + + 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 (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. |