diff options
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
-rw-r--r-- | Documentation/cpu-hotplug.txt | 49 |
1 files changed, 17 insertions, 32 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index 4d4a644b505e..a99d7031cdf9 100644 --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt | |||
@@ -315,41 +315,26 @@ A: The following are what is required for CPU hotplug infrastructure to work | |||
315 | 315 | ||
316 | Q: I need to ensure that a particular cpu is not removed when there is some | 316 | Q: I need to ensure that a particular cpu is not removed when there is some |
317 | work specific to this cpu is in progress. | 317 | work specific to this cpu is in progress. |
318 | A: First switch the current thread context to preferred cpu | 318 | A: There are two ways. If your code can be run in interrupt context, use |
319 | smp_call_function_single(), otherwise use work_on_cpu(). Note that | ||
320 | work_on_cpu() is slow, and can fail due to out of memory: | ||
319 | 321 | ||
320 | int my_func_on_cpu(int cpu) | 322 | int my_func_on_cpu(int cpu) |
321 | { | 323 | { |
322 | cpumask_t saved_mask, new_mask = CPU_MASK_NONE; | 324 | int err; |
323 | int curr_cpu, err = 0; | 325 | get_online_cpus(); |
324 | 326 | if (!cpu_online(cpu)) | |
325 | saved_mask = current->cpus_allowed; | 327 | err = -EINVAL; |
326 | cpu_set(cpu, new_mask); | 328 | else |
327 | err = set_cpus_allowed(current, new_mask); | 329 | #if NEEDS_BLOCKING |
328 | 330 | err = work_on_cpu(cpu, __my_func_on_cpu, NULL); | |
329 | if (err) | 331 | #else |
330 | return err; | 332 | smp_call_function_single(cpu, __my_func_on_cpu, &err, |
331 | 333 | true); | |
332 | /* | 334 | #endif |
333 | * If we got scheduled out just after the return from | 335 | put_online_cpus(); |
334 | * set_cpus_allowed() before running the work, this ensures | 336 | return err; |
335 | * we stay locked. | 337 | } |
336 | */ | ||
337 | curr_cpu = get_cpu(); | ||
338 | |||
339 | if (curr_cpu != cpu) { | ||
340 | err = -EAGAIN; | ||
341 | goto ret; | ||
342 | } else { | ||
343 | /* | ||
344 | * Do work : But cant sleep, since get_cpu() disables preempt | ||
345 | */ | ||
346 | } | ||
347 | ret: | ||
348 | put_cpu(); | ||
349 | set_cpus_allowed(current, saved_mask); | ||
350 | return err; | ||
351 | } | ||
352 | |||
353 | 338 | ||
354 | Q: How do we determine how many CPUs are available for hotplug. | 339 | Q: How do we determine how many CPUs are available for hotplug. |
355 | A: There is no clear spec defined way from ACPI that can give us that | 340 | A: There is no clear spec defined way from ACPI that can give us that |