Messages in this thread Patch in this message | | | From | Rusty Russell <> | Date | Tue, 3 Nov 2009 14:59:06 +1030 | Subject | [PATCH 14/14] cpumask: don't recommend set_cpus_allowed hack in Documentation/cpu-hotplug.txt |
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Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Ashok Raj <ashok.raj@intel.com> --- Documentation/cpu-hotplug.txt | 49 ++++++++++++++---------------------------- 1 file changed, 17 insertions(+), 32 deletions(-)
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -309,41 +309,26 @@ A: The following are what is required fo 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() 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; + cpu_hotplug_lock(); + 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 + cpu_hotplug_unlock(); + 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
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