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/*
* kernel/edf_common.c
*
* Common functions for EDF 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/edf_common.h>
#include <linux/hash.h>
#ifdef CONFIG_EDF_HASH_TIE_BREAK
static inline long edf_hash(struct task_struct *t)
{
long key;
/* pid is 32 bits, so normally we would shove that into the
* upper 32-bits and and put the job number in the bottom
* and hash the 64-bit number with hash_64(). Sadly,
* in testing, hash_64() doesn't distribute keys were the
* upper bits are close together (as would be the case with
* pids) and job numbers are equal (as would be the case with
* synchronous task sets with all relative deadlines equal).
*
* A 2006 Linux patch proposed the following solution
* (but for some reason it wasn't accepted...).
*
* At least this workaround works for 32-bit systems as well.
*/
/* This would be nice, but hash_64() has problems.
key = ((long)t->pid << 32) | ((long)tsk_rt(t)->job_params.job_no & 0xFFFFFFFF);
return hash_64(key, 0);
*/
return hash_32(hash_32((u32)tsk_rt(t)->job_params.job_no, 32) ^ t->pid, 32);
}
#endif
/* edf_higher_prio - returns true if first has a higher EDF priority
* than second. Deadline ties are broken by PID.
*
* both first and second may be NULL
*/
int edf_higher_prio(struct task_struct* first,
struct task_struct* second)
{
struct task_struct *first_task = first;
struct task_struct *second_task = second;
#ifdef CONFIG_EDF_HASH_TIE_BREAK
long fhash, shash;
#endif
/* There is no point in comparing a task to itself. */
if (first && first == second) {
TRACE_TASK(first,
"WARNING: pointless edf priority comparison.\n");
return 0;
}
/* check for NULL tasks */
if (!first || !second)
return first && !second;
#ifdef CONFIG_LITMUS_LOCKING
/* Check for inherited priorities. Change task
* used for comparison in such a case.
*/
if (unlikely(first->rt_param.inh_task))
first_task = first->rt_param.inh_task;
if (unlikely(second->rt_param.inh_task))
second_task = second->rt_param.inh_task;
/* Check for priority boosting. Tie-break by start of boosting.
*/
if (unlikely(is_priority_boosted(first_task))) {
/* first_task is boosted, how about second_task? */
if (!is_priority_boosted(second_task) ||
lt_before(get_boost_start(first_task),
get_boost_start(second_task)))
return 1;
else
return 0;
} else if (unlikely(is_priority_boosted(second_task)))
/* second_task is boosted, first is not*/
return 0;
#endif
return !is_realtime(second_task) ||
/* is the deadline of the first task earlier?
* Then it has higher priority.
*/
earlier_deadline(first_task, second_task) ||
/* Do we have a deadline tie?
* Then break by PID.
*/
(get_deadline(first_task) == get_deadline(second_task) &&
#ifdef CONFIG_EDF_HASH_TIE_BREAK
/* assignment within less-than compare is intentional */
((fhash = edf_hash(first_task)) < (shash = edf_hash(second_task)) ||
(fhash == shash &&
#endif
(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))
#ifdef CONFIG_EDF_HASH_TIE_BREAK
))
#endif
);
}
int edf_ready_order(struct bheap_node* a, struct bheap_node* b)
{
return edf_higher_prio(bheap2task(a), bheap2task(b));
}
void edf_domain_init(rt_domain_t* rt, check_resched_needed_t resched,
release_jobs_t release)
{
rt_domain_init(rt, edf_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 edf_preemption_needed(rt_domain_t* rt, struct task_struct *t)
{
/* we need the read lock for edf_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) || edf_higher_prio(__next_ready(rt), t);
}
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