diff options
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
| -rw-r--r-- | Documentation/cpu-hotplug.txt | 55 |
1 files changed, 23 insertions, 32 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index 9d620c153b0..a99d7031cdf 100644 --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -49,6 +49,12 @@ maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using additional_cpus=n (*) Use this to limit hotpluggable cpus. This option sets cpu_possible_map = cpu_present_map + additional_cpus +cede_offline={"off","on"} Use this option to disable/enable putting offlined + processors to an extended H_CEDE state on + supported pseries platforms. + If nothing is specified, + cede_offline is set to "on". + (*) Option valid only for following architectures - ia64 @@ -309,41 +315,26 @@ A: The following are what is required for CPU hotplug infrastructure to work 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 +A: There are two ways. If your code can be run in interrupt context, use + smp_call_function_single(), otherwise use work_on_cpu(). Note that + work_on_cpu() is slow, and can fail due to out of memory: 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 err; + get_online_cpus(); + if (!cpu_online(cpu)) + err = -EINVAL; + else +#if NEEDS_BLOCKING + err = work_on_cpu(cpu, __my_func_on_cpu, NULL); +#else + smp_call_function_single(cpu, __my_func_on_cpu, &err, + true); +#endif + put_online_cpus(); + return err; + } Q: How do we determine how many CPUs are available for hotplug. A: There is no clear spec defined way from ACPI that can give us that |