/*
* 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>
#ifdef CONFIG_EDF_TIE_BREAK_LATENESS_NORM
#include <litmus/fpmath.h>
#endif
#ifdef CONFIG_EDF_TIE_BREAK_HASH
#include <linux/hash.h>
static inline long edf_hash(struct task_struct *t)
{
/* 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.
*/
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;
/* 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
if (earlier_deadline(first_task, second_task)) {
return 1;
}
else if (get_deadline(first_task) == get_deadline(second_task)) {
/* Need to tie break. All methods must set pid_break to 0/1 if
* first_task does not have priority over second_task.
*/
int pid_break;
#if defined(CONFIG_EDF_TIE_BREAK_LATENESS)
/* Tie break by lateness. Jobs with greater lateness get
* priority. This should spread tardiness across all tasks,
* especially in task sets where all tasks have the same
* period and relative deadlines.
*/
if (get_lateness(first_task) > get_lateness(second_task)) {
return 1;
}
pid_break = (get_lateness(first_task) == get_lateness(second_task));
#elif defined(CONFIG_EDF_TIE_BREAK_LATENESS_NORM)
/* Tie break by lateness, normalized by relative deadline. Jobs with
* greater normalized lateness get priority.
*
* Note: Considered using the algebraically equivalent
* lateness(first)*relative_deadline(second) >
lateness(second)*relative_deadline(first)
* to avoid fixed-point math, but values are prone to overflow if inputs
* are on the order of several seconds, even in 64-bit.
*/
fp_t fnorm = _frac(get_lateness(first_task),
get_rt_relative_deadline(first_task));
fp_t snorm = _frac(get_lateness(second_task),
get_rt_relative_deadline(second_task));
if (_gt(fnorm, snorm)) {
return 1;
}
pid_break = _eq(fnorm, snorm);
#elif defined(CONFIG_EDF_TIE_BREAK_HASH)
/* Tie break by comparing hashs of (pid, job#) tuple. There should be
* a 50% chance that first_task has a higher priority than second_task.
*/
long fhash = edf_hash(first_task);
long shash = edf_hash(second_task);
if (fhash < shash) {
return 1;
}
pid_break = (fhash == shash);
#else
/* CONFIG_EDF_PID_TIE_BREAK */
pid_break = 1; // fall through to tie-break by pid;
#endif
/* Tie break by pid */
if(pid_break) {
if (first_task->pid < second_task->pid) {
return 1;
}
else if (first_task->pid == second_task->pid) {
/* If the PIDs are the same then the task with the
* inherited priority wins.
*/
if (!second->rt_param.inh_task) {
return 1;
}
}
}
}
return 0; /* fall-through. prio(second_task) > prio(first_task) */
}
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);
}
