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#include <linux/percpu.h>
#include <linux/hrtimer.h>
#include <litmus/litmus.h>
struct enforcement_timer {
/* The enforcement timer is used to accurately police
* slice budgets. */
struct hrtimer timer;
int armed;
};
DEFINE_PER_CPU(struct enforcement_timer, budget_timer);
static enum hrtimer_restart on_enforcement_timeout(struct hrtimer *timer)
{
struct enforcement_timer* et = container_of(timer,
struct enforcement_timer,
timer);
unsigned long flags;
local_irq_save(flags);
TRACE("enforcement timer fired.\n");
et->armed = 0;
/* activate scheduler */
set_tsk_need_resched(current);
local_irq_restore(flags);
return HRTIMER_NORESTART;
}
/* assumes called with IRQs off */
static void cancel_enforcement_timer(struct enforcement_timer* et)
{
int ret;
TRACE("cancelling enforcement timer.\n");
/* Since interrupts are disabled and et->armed is only
* modified locally, we do not need any locks.
*/
if (et->armed) {
ret = hrtimer_try_to_cancel(&et->timer);
/* Should never be inactive. */
BUG_ON(ret == 0);
/* Should never be running concurrently. */
BUG_ON(ret == -1);
et->armed = 0;
}
}
/* assumes called with IRQs off */
static void arm_enforcement_timer(struct enforcement_timer* et,
struct task_struct* t)
{
lt_t when_to_fire;
TRACE_TASK(t, "arming enforcement timer.\n");
/* Calling this when there is no budget left for the task
* makes no sense, unless the task is non-preemptive. */
BUG_ON(budget_exhausted(t) && (!is_np(t)));
/* __hrtimer_start_range_ns() cancels the timer
* anyway, so we don't have to check whether it is still armed */
if (likely(!is_np(t))) {
when_to_fire = litmus_clock() + budget_remaining(t);
__hrtimer_start_range_ns(&et->timer,
ns_to_ktime(when_to_fire),
0 /* delta */,
HRTIMER_MODE_ABS_PINNED,
0 /* no wakeup */);
et->armed = 1;
}
}
/* expects to be called with IRQs off */
void update_enforcement_timer(struct task_struct* t)
{
struct enforcement_timer* et = &__get_cpu_var(budget_timer);
if (t && budget_precisely_enforced(t)) {
/* Make sure we call into the scheduler when this budget
* expires. */
arm_enforcement_timer(et, t);
} else if (et->armed) {
/* Make sure we don't cause unnecessary interrupts. */
cancel_enforcement_timer(et);
}
}
static int __init init_budget_enforcement(void)
{
int cpu;
struct enforcement_timer* et;
for (cpu = 0; cpu < NR_CPUS; cpu++) {
et = &per_cpu(budget_timer, cpu);
hrtimer_init(&et->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
et->timer.function = on_enforcement_timeout;
}
return 0;
}
module_init(init_budget_enforcement);
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