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kernel: fix short time-slice reset

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The kernel tracks time slice usage with the _time_slice_elapsed global.
Every time the timer interrupt goes off and the timer driver calls
_nano_sys_clock_tick_announce() with the elapsed time, this is added to
_time_slice_elapsed. If it exceeds the total time slice, the thread is
moved to the back of the queue for that priority level and
_time_slice_elapsed is reset to zero.

In a non-tickless kernel, this is the only time _time_slice_elapsed is
reset.  If a thread uses up a partial time slice, and then cooperatively
switches to another thread, the next thread will inherit the remaining
time slice, causing it not to be able to run as long as it ought to.

There does exist code to properly reset the elapsed count, but it was
only compiled in a tickless kernel. Now it is built any time
CONFIG_TIMESLICING is enabled.

Issue: ZEP-2107
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2017-05-30 12:51:39 -07:00 • committed by Anas Nashif
commit 3989de7e3b
5 changed files with 10 additions and 20 deletions
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4
arch/arm/core/exc_exit.S
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@ -24,7 +24,7 @@ _ASM_FILE_PROLOGUE
GTEXT(_ExcExit)
GTEXT(_IntExit)
GDATA(_kernel)
#ifdef CONFIG_TICKLESS_KERNEL
#ifdef CONFIG_TIMESLICING
GTEXT(_update_time_slice_before_swap)
#endif
@ -58,7 +58,7 @@ SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _IntExit)
/* _IntExit falls through to _ExcExit (they are aliases of each other) */
#ifdef CONFIG_TICKLESS_KERNEL
#ifdef CONFIG_TIMESLICING
push {lr}
bl _update_time_slice_before_swap
#if defined(CONFIG_ARMV6_M)