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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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21
arch/arm/core/exc_exit.S
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@ -84,21 +84,14 @@ SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _ExcExit)
ldr r0, =_kernel
ldr r1, [r0, #_kernel_offset_to_current]
#ifdef CONFIG_CPU_CORTEX_M0_M0PLUS
movs r3, #_thread_offset_to_prio
ldrsb r2, [r1, r3]
#else
ldrsb r2, [r1, #_thread_offset_to_prio]
#endif
ldrb r3, [r1, #_thread_offset_to_sched_locked]
/* coop thread ? do not schedule */
cmp r2, #0
blt _EXIT_EXC
/* scheduler locked ? do not schedule */
cmp r3, #0
bne _EXIT_EXC
/*
* Non-preemptible thread ? Do not schedule (see explanation of
* preempt field in kernel_struct.h).
*/
ldrh r2, [r1, #_thread_offset_to_preempt]
cmp r2, #_PREEMPT_THRESHOLD
bhi _EXIT_EXC
ldr r0, [r0, _kernel_offset_to_ready_q_cache]
cmp r0, r1