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Fixes to the scheduler timeslice management.

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One is related to the time distribution when a new child is created.
If the parent has one tick left, then both child and parent received
zero tick. When combined with
	current_irq_nest_count = 1
	voluntary_preempt = 0
values, this caused the scheduler from being invoked.

Second is related to the overall time distribution. When a thread
runs out of time, its new time slice is calculated by the below
formula:
	new_timeslice = (thread_prio * SCHED_TICKS) / total_prio
If we consider total_prio is equal to the sum of the priorities of
all the threads in the system, it imposes a problem of getting
zero tick. In the new scenario, total_prio is equal to the priority
types in the system so it is fixed. Every thread gets a timeslice
in proportion of their priorities. Thus, there is no risk of taking
zero tick.
This commit is contained in:
Bora Sahin
2009-10-18 20:20:40 +03:00
committed by Bahadir Balban
parent 90cfaca7a2
commit 2571dabc18
3 changed files with 7 additions and 7 deletions
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5
src/api/thread.c
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@@ -256,8 +256,9 @@ int arch_setup_new_thread(struct ktcb *new, struct ktcb *orig,
new->context.pc = orig->syscall_regs->lr_usr;
/* Distribute original thread's ticks into two threads */
new->ticks_left = orig->ticks_left / 2;
orig->ticks_left /= 2;
new->ticks_left = (orig->ticks_left + 1) >> 1;
if (!(orig->ticks_left >>= 1))
orig->ticks_left = 1;
return 0;
}