preempt_disable() - disables preemption on all processors?

[Rajat Jain]

Hi list,

Does the preempt_disable() disable preemption on all the processors or just the current processor?

Thanks,

Rajat

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[Mulyadi Santosa]

HI...

Post by Rajat Jain
Does the preempt_disable() disable preemption on all the processors or just the current processor?

Fast check on schedule() code makes me believe it just disables the
preemption on current processor which call preempt_disable().

regards,

Mulyadi
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[Ricardo Maraschini]

And the get_cpu() ? Its not supposed to disable preemption in all cpus?
from include/linux/smp.h:

#define get_cpu() ({ preempt_disable(); smp_processor_id(); })

rjm;

Post by Rajat Jain
HI...

Post by Rajat Jain
Does the preempt_disable() disable preemption on all the processors or

just the current processor?
Fast check on schedule() code makes me believe it just disables the
preemption on current processor which call preempt_disable().
regards,
Mulyadi
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[Mulyadi Santosa]

Hi...

Post by Ricardo Maraschini
And the get_cpu() ? Its not supposed to disable preemption in all cpus?
#define get_cpu() ({ preempt_disable(); smp_processor_id(); })

Same thing, only for current CPU with executes the code path that calls
preempt_enable/disable(). You can check the definition of
preempt_count() in {kerneldir}/include/linux/smp.h:

#define preempt_count() (current_thread_info()->preempt_count)


There, you'll see that the preemption flag is actually tied to current
task_struct's stack. Since a task run on a processor at a time, I follow
the same logic that preemption is also enabled/disabled for current
processor only.

regards,

Mulyadi.


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