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Processor affinity settings for Linux kernel modules?

Answer 1

+1 A:

I think you'll probably have to modify the kernel, but the change isn't too rough. Just export sched_setaffinity in sched.c to modules:

  long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
  {
    ...
  }
+ EXPORT_SYMBOL_GPL(sched_setaffinity); // Exported, now callable from your code.

John Feminella 2010-06-13 18:57:30

I've seen this before and assumed it was only meant for userland processes, however if I set the pid argument to 0 it actually works.I managed to do it without recompiling the kernel using a function pointer and looking up sched_setaffinity in /boot/System.map, just for testing it out.long (*extern_sched_setaffinity)(pid_t pid, const struct cpumask *in_mask) = (void*)0xffffffff81066a70; on my system.Thanks.

Stephen Pape 2010-06-13 19:15:51

This isn't likely to be a good idea, unless you're just setting the affinity of a kernel thread created specifically by your driver. Otherwise, driver code can run in the context of many different processes at different times, each of which has its *own* scheduler affinity. If you just want to execute a short section of code without being bounced to another CPU, you can use `preempt_disable()` and `preempt_enable()` to create a preemption-disabled critical section.

caf 2010-06-16 07:36:56

@caf: I assumed that what you described is the case, because he says "my code". Good advice in any case, though.

John Feminella 2010-06-16 10:11:37

Answer 2

+1 A:

smp_processor_id() should tell you what logical processor you're running on.

Some architectures also support the smp_call_function_single kernel function that will use an inter-processor-interrupt to run a function on another processor.

Eric Seppanen 2010-06-15 16:53:19

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Processor affinity settings for Linux kernel modules?

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