Commit 4251417484a1775ba5cbfe38c67e6d5af9615de4
1 parent
62ac127950
Exists in
master
and in
20 other branches
cpumask: don't recommend set_cpus_allowed hack in Documentation/cpu-hotplug.txt
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Ashok Raj <ashok.raj@intel.com>
Showing 1 changed file with 17 additions and 32 deletions Side-by-side Diff
Documentation/cpu-hotplug.txt
| ... | ... | @@ -315,41 +315,26 @@ |
| 315 | 315 | |
| 316 | 316 | Q: I need to ensure that a particular cpu is not removed when there is some |
| 317 | 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 | 322 | int my_func_on_cpu(int cpu) |
| 321 | 323 | { |
| 322 | - cpumask_t saved_mask, new_mask = CPU_MASK_NONE; | |
| 323 | - int curr_cpu, err = 0; | |
| 324 | - | |
| 325 | - saved_mask = current->cpus_allowed; | |
| 326 | - cpu_set(cpu, new_mask); | |
| 327 | - err = set_cpus_allowed(current, new_mask); | |
| 328 | - | |
| 329 | - if (err) | |
| 330 | - return err; | |
| 331 | - | |
| 332 | - /* | |
| 333 | - * If we got scheduled out just after the return from | |
| 334 | - * set_cpus_allowed() before running the work, this ensures | |
| 335 | - * we stay locked. | |
| 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 | - | |
| 324 | + int err; | |
| 325 | + get_online_cpus(); | |
| 326 | + if (!cpu_online(cpu)) | |
| 327 | + err = -EINVAL; | |
| 328 | + else | |
| 329 | +#if NEEDS_BLOCKING | |
| 330 | + err = work_on_cpu(cpu, __my_func_on_cpu, NULL); | |
| 331 | +#else | |
| 332 | + smp_call_function_single(cpu, __my_func_on_cpu, &err, | |
| 333 | + true); | |
| 334 | +#endif | |
| 335 | + put_online_cpus(); | |
| 336 | + return err; | |
| 337 | + } | |
| 353 | 338 | |
| 354 | 339 | Q: How do we determine how many CPUs are available for hotplug. |
| 355 | 340 | A: There is no clear spec defined way from ACPI that can give us that |