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kernel/arch: inspect prio/sched_locked together for preemptibility

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These two fields in the thread structure control the preemptibility of a
thread.

sched_locked is decremented when the scheduler gets locked, which means
that the scheduler is locked for values 0xff to 0x01, since it can be
locked recursively. A thread is coop if its priority is negative, thus
if the prio field value is 0x80 to 0xff when looked at as an unsigned
value.

By putting them end-to-end, this means that a thread is non-preemptible
if the bundled value is greater than or equal to 0x0080. This is the
only thing the interrupt exit code has to check to decide to try a
reschedule or not.

Change-Id: I902d36c14859d0d7a951a6aa1bea164613821aca
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>
This commit is contained in:
Benjamin Walsh 2016-12-21 16:00:35 -05:00 • committed by Anas Nashif
commit 168695c7ef
10 changed files with 80 additions and 77 deletions
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3
kernel/include/ksched.h
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@ -146,7 +146,8 @@ static inline int _is_coop(struct k_thread *thread)
static inline int _is_preempt(struct k_thread *thread)
{
#ifdef CONFIG_PREEMPT_ENABLED
return !_is_coop(thread) && !thread->base.sched_locked;
/* explanation in kernel_struct.h */
return thread->base.preempt <= _PREEMPT_THRESHOLD;
#else
return 0;
#endif