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Subject[PATCH] 2.6.0-test4 scheduler policy
Hi Linux kernel,
Please find attached my CPU scheduler changes against test4. A few
bugs have been fixed up. The known problems are test-starve.c, bad
for compute intensive loads, bad priority distribution (eg. may cause
xmms to skip. must be a bug somewhere).

This is mainly a sync with Linus' tree.

--- linux-2.6/include/linux/sched.h.orig 2003-08-23 19:35:43.000000000 +1000
+++ linux-2.6/include/linux/sched.h 2003-08-23 19:50:28.000000000 +1000
@@ -281,7 +281,9 @@ struct signal_struct {
#define MAX_RT_PRIO MAX_USER_RT_PRIO

#define MAX_PRIO (MAX_RT_PRIO + 40)
-
+
+#define rt_task(p) ((p)->prio < MAX_RT_PRIO)
+
/*
* Some day this will be a full-fledged user tracking system..
*/
@@ -339,12 +341,15 @@ struct task_struct {
struct list_head run_list;
prio_array_t *array;

+ unsigned long array_sequence;
+ unsigned long timestamp;
+
unsigned long sleep_avg;
- unsigned long last_run;

unsigned long policy;
cpumask_t cpus_allowed;
unsigned int time_slice, first_time_slice;
+ unsigned int used_slice;

struct list_head tasks;
struct list_head ptrace_children;
--- linux-2.6/kernel/fork.c.orig 2003-08-23 19:35:36.000000000 +1000
+++ linux-2.6/kernel/fork.c 2003-08-23 19:50:28.000000000 +1000
@@ -917,14 +917,14 @@ struct task_struct *copy_process(unsigne
* resulting in more scheduling fairness.
*/
local_irq_disable();
- p->time_slice = (current->time_slice + 1) >> 1;
+ p->timestamp = jiffies;
+ p->time_slice = (current->time_slice + 2) / 3;
/*
* The remainder of the first timeslice might be recovered by
* the parent if the child exits early enough.
*/
p->first_time_slice = 1;
- current->time_slice >>= 1;
- p->last_run = jiffies;
+ current->time_slice = 2 * current->time_slice / 3;
if (!current->time_slice) {
/*
* This case is rare, it happens when the parent has only
--- linux-2.6/kernel/sched.c.orig 2003-08-23 19:35:32.000000000 +1000
+++ linux-2.6/kernel/sched.c 2003-08-23 21:40:34.000000000 +1000
@@ -60,78 +60,52 @@
#define MAX_USER_PRIO (USER_PRIO(MAX_PRIO))

/*
+ * Some helpers for converting nanosecond timing to jiffy resolution
+ */
+#define NS_TO_JIFFIES(TIME) (TIME / (1000000000 / HZ))
+#define JIFFIES_TO_NS(TIME) (TIME * (1000000000 / HZ))
+
+#define US_TO_JIFFIES(TIME) (TIME / (1000000 / HZ))
+#define JIFFIES_TO_US(TIME) (TIME * (1000000 / HZ))
+
+#define NS_TO_US(TIME) (TIME / 1000)
+#define US_TO_NS(TIME) (TIME * 1000)
+
+/*
* These are the 'tuning knobs' of the scheduler:
*
* Minimum timeslice is 10 msecs, default timeslice is 100 msecs,
* maximum timeslice is 200 msecs. Timeslices get refilled after
* they expire.
*/
-#define MIN_TIMESLICE ( 10 * HZ / 1000)
-#define MAX_TIMESLICE (200 * HZ / 1000)
-#define CHILD_PENALTY 50
-#define PARENT_PENALTY 100
-#define EXIT_WEIGHT 3
-#define PRIO_BONUS_RATIO 25
-#define INTERACTIVE_DELTA 2
-#define MAX_SLEEP_AVG (10*HZ)
-#define STARVATION_LIMIT (10*HZ)
-#define NODE_THRESHOLD 125
-
-/*
- * If a task is 'interactive' then we reinsert it in the active
- * array after it has expired its current timeslice. (it will not
- * continue to run immediately, it will still roundrobin with
- * other interactive tasks.)
- *
- * This part scales the interactivity limit depending on niceness.
- *
- * We scale it linearly, offset by the INTERACTIVE_DELTA delta.
- * Here are a few examples of different nice levels:
- *
- * TASK_INTERACTIVE(-20): [1,1,1,1,1,1,1,1,1,0,0]
- * TASK_INTERACTIVE(-10): [1,1,1,1,1,1,1,0,0,0,0]
- * TASK_INTERACTIVE( 0): [1,1,1,1,0,0,0,0,0,0,0]
- * TASK_INTERACTIVE( 10): [1,1,0,0,0,0,0,0,0,0,0]
- * TASK_INTERACTIVE( 19): [0,0,0,0,0,0,0,0,0,0,0]
- *
- * (the X axis represents the possible -5 ... 0 ... +5 dynamic
- * priority range a task can explore, a value of '1' means the
- * task is rated interactive.)
- *
- * Ie. nice +19 tasks can never get 'interactive' enough to be
- * reinserted into the active array. And only heavily CPU-hog nice -20
- * tasks will be expired. Default nice 0 tasks are somewhere between,
- * it takes some effort for them to get interactive, but it's not
- * too hard.
- */
+#define MIN_TIMESLICE (10 * HZ / 1000)
+#define MAX_TIMESLICE (100 * HZ / 1000)

-#define SCALE(v1,v1_max,v2_max) \
- (v1) * (v2_max) / (v1_max)
+#define MAX_SLEEP_AVG (HZ)

-#define DELTA(p) \
- (SCALE(TASK_NICE(p), 40, MAX_USER_PRIO*PRIO_BONUS_RATIO/100) + \
- INTERACTIVE_DELTA)
+#define NODE_THRESHOLD 125

-#define TASK_INTERACTIVE(p) \
- ((p)->prio <= (p)->static_prio - DELTA(p))
+#define TASK_PREEMPTS_CURR(p, rq) \
+ ((p)->prio < (rq)->curr->prio)

/*
- * BASE_TIMESLICE scales user-nice values [ -20 ... 19 ]
- * to time slice values.
- *
* The higher a thread's priority, the bigger timeslices
* it gets during one round of execution. But even the lowest
* priority thread gets MIN_TIMESLICE worth of execution time.
- *
- * task_timeslice() is the interface that is used by the scheduler.
*/
-
-#define BASE_TIMESLICE(p) (MIN_TIMESLICE + \
- ((MAX_TIMESLICE - MIN_TIMESLICE) * (MAX_PRIO-1-(p)->static_prio)/(MAX_USER_PRIO - 1)))
-
static inline unsigned int task_timeslice(task_t *p)
{
- return BASE_TIMESLICE(p);
+ unsigned int timeslice = MIN_TIMESLICE +
+ ( (MAX_USER_PRIO - USER_PRIO(p->prio))
+ * (MAX_TIMESLICE - MIN_TIMESLICE) )
+ / MAX_USER_PRIO;
+
+ if (timeslice < MIN_TIMESLICE)
+ timeslice = MIN_TIMESLICE;
+ if (timeslice > MAX_TIMESLICE)
+ timeslice = MAX_TIMESLICE;
+
+ return timeslice;
}

/*
@@ -157,7 +131,8 @@ struct prio_array {
*/
struct runqueue {
spinlock_t lock;
- unsigned long nr_running, nr_switches, expired_timestamp,
+ unsigned long array_sequence;
+ unsigned long nr_running, nr_switches,
nr_uninterruptible;
task_t *curr, *idle;
struct mm_struct *prev_mm;
@@ -179,7 +154,6 @@ static DEFINE_PER_CPU(struct runqueue, r
#define this_rq() (&__get_cpu_var(runqueues))
#define task_rq(p) cpu_rq(task_cpu(p))
#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
-#define rt_task(p) ((p)->prio < MAX_RT_PRIO)

/*
* Default context-switch locking:
@@ -298,35 +272,22 @@ static inline void enqueue_task(struct t
p->array = array;
}

-/*
- * effective_prio - return the priority that is based on the static
- * priority but is modified by bonuses/penalties.
- *
- * We scale the actual sleep average [0 .... MAX_SLEEP_AVG]
- * into the -5 ... 0 ... +5 bonus/penalty range.
- *
- * We use 25% of the full 0...39 priority range so that:
- *
- * 1) nice +19 interactive tasks do not preempt nice 0 CPU hogs.
- * 2) nice -20 CPU hogs do not get preempted by nice 0 tasks.
- *
- * Both properties are important to certain workloads.
- */
-static int effective_prio(task_t *p)
+static unsigned long task_priority(task_t *p)
{
int bonus, prio;

if (rt_task(p))
return p->prio;

- bonus = MAX_USER_PRIO*PRIO_BONUS_RATIO*p->sleep_avg/MAX_SLEEP_AVG/100 -
- MAX_USER_PRIO*PRIO_BONUS_RATIO/100/2;
+ bonus = (MAX_USER_PRIO * p->sleep_avg) / MAX_SLEEP_AVG / 2;
+ prio = USER_PRIO(p->static_prio) + (MAX_USER_PRIO / 4);

- prio = p->static_prio - bonus;
+ prio = MAX_RT_PRIO + prio - bonus;
if (prio < MAX_RT_PRIO)
prio = MAX_RT_PRIO;
if (prio > MAX_PRIO-1)
prio = MAX_PRIO-1;
+
return prio;
}

@@ -347,34 +308,39 @@ static inline void __activate_task(task_
*/
static inline void activate_task(task_t *p, runqueue_t *rq)
{
- long sleep_time = jiffies - p->last_run - 1;
+ unsigned long now = jiffies;
+ unsigned long s = now - p->timestamp;

- if (sleep_time > 0) {
- int sleep_avg;
+ if (s > MAX_SLEEP_AVG)
+ s = MAX_SLEEP_AVG;

- /*
- * This code gives a bonus to interactive tasks.
- *
- * The boost works by updating the 'average sleep time'
- * value here, based on ->last_run. The more time a task
- * spends sleeping, the higher the average gets - and the
- * higher the priority boost gets as well.
- */
- sleep_avg = p->sleep_avg + sleep_time;
+ if (!in_interrupt() && current->mm) {
+ unsigned long boost = s/2;
+ if (current->sleep_avg + boost > MAX_SLEEP_AVG)
+ boost = MAX_SLEEP_AVG - current->sleep_avg;
+ current->sleep_avg += boost;
+ p->sleep_avg += s - boost;
+ } else
+ p->sleep_avg += s;

- /*
- * 'Overflow' bonus ticks go to the waker as well, so the
- * ticks are not lost. This has the effect of further
- * boosting tasks that are related to maximum-interactive
- * tasks.
- */
- if (sleep_avg > MAX_SLEEP_AVG)
- sleep_avg = MAX_SLEEP_AVG;
- if (p->sleep_avg != sleep_avg) {
- p->sleep_avg = sleep_avg;
- p->prio = effective_prio(p);
- }
+ if (p->sleep_avg > MAX_SLEEP_AVG)
+ p->sleep_avg = MAX_SLEEP_AVG;
+
+ p->prio = task_priority(p);
+
+ if (rq->array_sequence != p->array_sequence) {
+ p->used_slice = 0;
+ p->time_slice = task_timeslice(p);
+ }
+
+ if (!in_interrupt() && current->mm) {
+ unsigned long steal;
+ steal = min((unsigned int)s / 2,
+ (p->time_slice - p->used_slice) / 2);
+ p->time_slice -= steal;
+ current->time_slice += steal;
}
+
__activate_task(p, rq);
}

@@ -383,10 +349,12 @@ static inline void activate_task(task_t
*/
static inline void deactivate_task(struct task_struct *p, runqueue_t *rq)
{
+ p->array_sequence = rq->array_sequence;
nr_running_dec(rq);
if (p->state == TASK_UNINTERRUPTIBLE)
rq->nr_uninterruptible++;
dequeue_task(p, p->array);
+ p->timestamp = jiffies;
p->array = NULL;
}

@@ -426,7 +394,7 @@ static inline void resched_task(task_t *
* be called with interrupts off, or it may introduce deadlock with
* smp_call_function() if an IPI is sent by the same process we are
* waiting to become inactive.
- */
+ n*/
void wait_task_inactive(task_t * p)
{
unsigned long flags;
@@ -497,11 +465,9 @@ repeat_lock_task:
}
if (old_state == TASK_UNINTERRUPTIBLE)
rq->nr_uninterruptible--;
- if (sync)
- __activate_task(p, rq);
- else {
- activate_task(p, rq);
- if (p->prio < rq->curr->prio)
+ activate_task(p, rq);
+ if (!sync) {
+ if (TASK_PREEMPTS_CURR(p, rq))
resched_task(rq->curr);
}
success = 1;
@@ -539,31 +505,30 @@ int wake_up_state(task_t *p, unsigned in
* This function will do some initial scheduler statistics housekeeping
* that must be done for every newly created process.
*/
-void wake_up_forked_process(task_t * p)
+void wake_up_forked_process(task_t *p)
{
unsigned long flags;
runqueue_t *rq = task_rq_lock(current, &flags);

p->state = TASK_RUNNING;
- /*
- * We decrease the sleep average of forking parents
- * and children as well, to keep max-interactive tasks
- * from forking tasks that are max-interactive.
- */
- current->sleep_avg = current->sleep_avg * PARENT_PENALTY / 100;
- p->sleep_avg = p->sleep_avg * CHILD_PENALTY / 100;
- p->prio = effective_prio(p);
+
set_task_cpu(p, smp_processor_id());

- if (unlikely(!current->array))
- __activate_task(p, rq);
- else {
- p->prio = current->prio;
- list_add_tail(&p->run_list, &current->run_list);
- p->array = current->array;
- p->array->nr_active++;
- nr_running_inc(rq);
- }
+#if 0
+ current->sleep_time = 3 * (current->sleep_time) / 4;
+ if (current->total_time != 0)
+ current->sleep_avg = (100 * current->sleep_time)
+ / current->total_time;
+ p->sleep_time = current->sleep_time / 4;
+ p->total_time = current->total_time / 4;
+ p->sleep_avg = current->sleep_avg;
+#endif
+ p->sleep_avg = 4 * current->sleep_avg / 5;
+ current->sleep_avg = 3 * current->sleep_avg / 4;
+
+ p->prio = task_priority(p);
+ __activate_task(p, rq);
+
task_rq_unlock(rq, &flags);
}

@@ -581,19 +546,9 @@ void sched_exit(task_t * p)
unsigned long flags;

local_irq_save(flags);
- if (p->first_time_slice) {
- p->parent->time_slice += p->time_slice;
- if (unlikely(p->parent->time_slice > MAX_TIMESLICE))
- p->parent->time_slice = MAX_TIMESLICE;
- }
+ if (p->first_time_slice)
+ p->parent->time_slice += p->time_slice - p->used_slice;
local_irq_restore(flags);
- /*
- * If the child was a (relative-) CPU hog then decrease
- * the sleep_avg of the parent as well.
- */
- if (p->sleep_avg < p->parent->sleep_avg)
- p->parent->sleep_avg = (p->parent->sleep_avg * EXIT_WEIGHT +
- p->sleep_avg) / (EXIT_WEIGHT + 1);
}

/**
@@ -995,13 +950,29 @@ static inline void pull_task(runqueue_t
* Note that idle threads have a prio of MAX_PRIO, for this test
* to be always true for them.
*/
- if (p->prio < this_rq->curr->prio)
+ if (TASK_PREEMPTS_CURR(p, this_rq))
set_need_resched();
- else {
- if (p->prio == this_rq->curr->prio &&
- p->time_slice > this_rq->curr->time_slice)
- set_need_resched();
- }
+}
+
+/*
+ * comment me
+ */
+
+static inline int
+can_migrate_task(task_t *tsk, runqueue_t *rq, int this_cpu, int idle)
+{
+ unsigned long delta;
+
+ if (task_running(rq, tsk))
+ return 0;
+ if (!cpu_isset(this_cpu, tsk->cpus_allowed))
+ return 0;
+
+ delta = jiffies - tsk->timestamp;
+ if (idle && (delta <= cache_decay_ticks))
+ return 0;
+
+ return 1;
}

/*
@@ -1063,14 +1034,9 @@ skip_queue:
* 3) are cache-hot on their current CPU.
*/

-#define CAN_MIGRATE_TASK(p,rq,this_cpu) \
- ((!idle || (jiffies - (p)->last_run > cache_decay_ticks)) && \
- !task_running(rq, p) && \
- cpu_isset(this_cpu, (p)->cpus_allowed))
-
curr = curr->prev;

- if (!CAN_MIGRATE_TASK(tmp, busiest, this_cpu)) {
+ if (!can_migrate_task(tmp, busiest, this_cpu, idle)) {
if (curr != head)
goto skip_queue;
idx++;
@@ -1171,20 +1137,6 @@ DEFINE_PER_CPU(struct kernel_stat, kstat
EXPORT_PER_CPU_SYMBOL(kstat);

/*
- * We place interactive tasks back into the active array, if possible.
- *
- * To guarantee that this does not starve expired tasks we ignore the
- * interactivity of a task if the first expired task had to wait more
- * than a 'reasonable' amount of time. This deadline timeout is
- * load-dependent, as the frequency of array switched decreases with
- * increasing number of running tasks:
- */
-#define EXPIRED_STARVING(rq) \
- (STARVATION_LIMIT && ((rq)->expired_timestamp && \
- (jiffies - (rq)->expired_timestamp >= \
- STARVATION_LIMIT * ((rq)->nr_running) + 1)))
-
-/*
* This function gets called by the timer code, with HZ frequency.
* We call it with interrupts disabled.
*
@@ -1201,17 +1153,11 @@ void scheduler_tick(int user_ticks, int
if (rcu_pending(cpu))
rcu_check_callbacks(cpu, user_ticks);

- /* note: this timer irq context must be accounted for as well */
- if (hardirq_count() - HARDIRQ_OFFSET) {
- cpustat->irq += sys_ticks;
- sys_ticks = 0;
- } else if (softirq_count()) {
- cpustat->softirq += sys_ticks;
- sys_ticks = 0;
- }
-
if (p == rq->idle) {
- if (atomic_read(&rq->nr_iowait) > 0)
+ /* note: this timer irq context must be accounted for as well */
+ if (irq_count() - HARDIRQ_OFFSET >= SOFTIRQ_OFFSET)
+ cpustat->system += sys_ticks;
+ else if (atomic_read(&rq->nr_iowait) > 0)
cpustat->iowait += sys_ticks;
else
cpustat->idle += sys_ticks;
@@ -1232,43 +1178,41 @@ void scheduler_tick(int user_ticks, int
spin_lock(&rq->lock);
/*
* The task was running during this tick - update the
- * time slice counter and the sleep average. Note: we
- * do not update a thread's priority until it either
- * goes to sleep or uses up its timeslice. This makes
- * it possible for interactive tasks to use up their
- * timeslices at their highest priority levels.
+ * time slice counter. Note: we do not update a thread's
+ * priority until it either goes to sleep or uses up its
+ * timeslice.
*/
- if (p->sleep_avg)
- p->sleep_avg--;
if (unlikely(rt_task(p))) {
/*
* RR tasks need a special form of timeslice management.
* FIFO tasks have no timeslices.
*/
- if ((p->policy == SCHED_RR) && !--p->time_slice) {
- p->time_slice = task_timeslice(p);
- p->first_time_slice = 0;
- set_tsk_need_resched(p);
-
- /* put it at the end of the queue: */
- dequeue_task(p, rq->active);
- enqueue_task(p, rq->active);
+ if (p->policy == SCHED_RR) {
+ p->used_slice++;
+ if (p->used_slice >= p->time_slice) {
+ p->used_slice = 0;
+ p->time_slice = task_timeslice(p);
+ p->first_time_slice = 0;
+ set_tsk_need_resched(p);
+
+ /* put it at the end of the queue: */
+ dequeue_task(p, rq->active);
+ enqueue_task(p, rq->active);
+ }
}
goto out_unlock;
}
- if (!--p->time_slice) {
+
+ p->used_slice++;
+ if (p->used_slice >= p->time_slice) {
dequeue_task(p, rq->active);
set_tsk_need_resched(p);
- p->prio = effective_prio(p);
+ p->prio = task_priority(p);
p->time_slice = task_timeslice(p);
+ p->used_slice = 0;
p->first_time_slice = 0;

- if (!TASK_INTERACTIVE(p) || EXPIRED_STARVING(rq)) {
- if (!rq->expired_timestamp)
- rq->expired_timestamp = jiffies;
- enqueue_task(p, rq->expired);
- } else
- enqueue_task(p, rq->active);
+ enqueue_task(p, rq->expired);
}
out_unlock:
spin_unlock(&rq->lock);
@@ -1287,6 +1231,8 @@ asmlinkage void schedule(void)
runqueue_t *rq;
prio_array_t *array;
struct list_head *queue;
+ unsigned long now;
+ unsigned long run_time;
int idx;

/*
@@ -1307,7 +1253,13 @@ need_resched:
rq = this_rq();

release_kernel_lock(prev);
- prev->last_run = jiffies;
+ now = jiffies;
+ run_time = now - prev->timestamp;
+ if (prev->sleep_avg <= run_time)
+ prev->sleep_avg = 0;
+ else
+ prev->sleep_avg -= run_time;
+
spin_lock_irq(&rq->lock);

/*
@@ -1336,7 +1288,6 @@ pick_next_task:
goto pick_next_task;
#endif
next = rq->idle;
- rq->expired_timestamp = 0;
goto switch_tasks;
}

@@ -1345,10 +1296,10 @@ pick_next_task:
/*
* Switch the active and expired arrays.
*/
+ rq->array_sequence++;
rq->active = rq->expired;
rq->expired = array;
array = rq->active;
- rq->expired_timestamp = 0;
}

idx = sched_find_first_bit(array->bitmap);
@@ -1361,6 +1312,7 @@ switch_tasks:
RCU_qsctr(task_cpu(prev))++;

if (likely(prev != next)) {
+ next->timestamp = now;
rq->nr_switches++;
rq->curr = next;

@@ -1600,6 +1552,7 @@ void set_user_nice(task_t *p, long nice)
unsigned long flags;
prio_array_t *array;
runqueue_t *rq;
+ int old_prio, new_prio, delta;

if (TASK_NICE(p) == nice || nice < -20 || nice > 19)
return;
@@ -1608,6 +1561,12 @@ void set_user_nice(task_t *p, long nice)
* the task might be in the middle of scheduling on another CPU.
*/
rq = task_rq_lock(p, &flags);
+ /*
+ * The RT priorities are set via setscheduler(), but we still
+ * allow the 'normal' nice value to be set - but as expected
+ * it wont have any effect on scheduling until the task is
+ * not SCHED_NORMAL:
+ */
if (rt_task(p)) {
p->static_prio = NICE_TO_PRIO(nice);
goto out_unlock;
@@ -1615,16 +1574,20 @@ void set_user_nice(task_t *p, long nice)
array = p->array;
if (array)
dequeue_task(p, array);
+
+ old_prio = p->prio;
+ new_prio = NICE_TO_PRIO(nice);
+ delta = new_prio - old_prio;
p->static_prio = NICE_TO_PRIO(nice);
- p->prio = NICE_TO_PRIO(nice);
+ p->prio += delta;
+
if (array) {
enqueue_task(p, array);
/*
- * If the task is running and lowered its priority,
- * or increased its priority then reschedule its CPU:
+ * If the task increased its priority or is running and
+ * lowered its priority, then reschedule its CPU:
*/
- if ((NICE_TO_PRIO(nice) < p->static_prio) ||
- task_running(rq, p))
+ if (delta < 0 || (delta > 0 && task_running(rq, p)))
resched_task(rq->curr);
}
out_unlock:
\
 
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