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/*
* kernel/rm_common.c
*
* Common functions for RM based scheduler.
*/
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/list.h>
#include <litmus/litmus.h>
#include <litmus/sched_plugin.h>
#include <litmus/sched_trace.h>
#include <litmus/rm_common.h>
/* rm_higher_prio - returns true if first has a higher RM priority
* than second. Deadline ties are broken by PID.
*
* both first and second may be NULL
*/
int rm_higher_prio(struct task_struct* first,
struct task_struct* second)
{
struct task_struct *first_task = first;
struct task_struct *second_task = second;
/* There is no point in comparing a task to itself. */
if (first && first == second) {
TRACE_TASK(first,
"WARNING: pointless rm priority comparison.\n");
return 0;
}
/* check for NULL tasks */
if (!first || !second)
return first && !second;
return !is_realtime(second_task) ||
/* is the deadline of the first task earlier?
* Then it has higher priority.
*/
lt_before(get_rt_period(first_task), get_rt_period(second_task)) ||
/* Do we have a deadline tie?
* Then break by PID.
*/
(get_rt_period(first_task) == get_rt_period(second_task) &&
(first_task->pid < second_task->pid ||
/* If the PIDs are the same then the task with the inherited
* priority wins.
*/
(first_task->pid == second_task->pid &&
!second->rt_param.inh_task)));
}
int rm_ready_order(struct bheap_node* a, struct bheap_node* b)
{
return rm_higher_prio(bheap2task(a), bheap2task(b));
}
void rm_domain_init(rt_domain_t* rt, check_resched_needed_t resched,
release_jobs_t release)
{
rt_domain_init(rt, rm_ready_order, resched, release);
}
/* need_to_preempt - check whether the task t needs to be preempted
* call only with irqs disabled and with ready_lock acquired
* THIS DOES NOT TAKE NON-PREEMPTIVE SECTIONS INTO ACCOUNT!
*/
int rm_preemption_needed(rt_domain_t* rt, struct task_struct *t)
{
/* we need the read lock for rm_ready_queue */
/* no need to preempt if there is nothing pending */
if (!__jobs_pending(rt))
return 0;
/* we need to reschedule if t doesn't exist */
if (!t)
return 1;
/* NOTE: We cannot check for non-preemptibility since we
* don't know what address space we're currently in.
*/
/* make sure to get non-rt stuff out of the way */
return !is_realtime(t) || rm_higher_prio(__next_ready(rt), t);
}
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