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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
Download Patch File Download Diff File Expand all files Collapse all files

3
include/l4/generic/scheduler.h
View File

@@ -17,6 +17,7 @@
#define TASK_PRIO_SERVER 6
#define TASK_PRIO_NORMAL 4
#define TASK_PRIO_LOW 2
#define TASK_PRIO_TOTAL 30
/* Ticks per second, try ticks = 1000 + timeslice = 1 for regressed preemption test. */
#define SCHED_TICKS 100
@@ -25,7 +26,7 @@
* A task can run continuously at this granularity,
* even if it has a greater total time slice.
*/
#define SCHED_GRANULARITY SCHED_TICKS/10
#define SCHED_GRANULARITY SCHED_TICKS/50
static inline struct ktcb *current_task(void)
{

5
src/api/thread.c
View File

@@ -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;
}

6
src/generic/scheduler.c
View File

@@ -119,7 +119,7 @@ void sched_init(struct scheduler *scheduler)
scheduler->rq_runnable = &scheduler->sched_rq[0];
scheduler->rq_expired = &scheduler->sched_rq[1];
scheduler->prio_total = 0;
scheduler->prio_total = TASK_PRIO_TOTAL;
}
/* Swap runnable and expired runqueues. */
@@ -463,10 +463,8 @@ void schedule()
}
/* New tasks affect runqueue total priority. */
if (next->flags & TASK_RESUMING) {
scheduler.prio_total += next->priority;
if (next->flags & TASK_RESUMING)
next->flags &= ~TASK_RESUMING;
}
/* Zero ticks indicates task hasn't ran since last rq swap */
if (next->ticks_left == 0) {