Messages in this thread Patch in this message | | | Date | Wed, 21 Dec 2005 16:21:41 +1100 | From | Peter Williams <> | Subject | Re: [PATCH] cpu scheduler: unsquish dynamic priorities |
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Peter Williams wrote: > The problem: > > The current scheduler implementation maps 40 nice values and 10 bonus > values into only 40 priority slots on the run queues. This results in > the dynamic priorities of tasks at either end of the nice scale being > squished up. E.g. all tasks with nice in the range -20 to -16 and the > maximum of 10 bonus points will end up with a dynamic priority of > MAX_RT_PRIO and all tasks with nice in the range 15 to 19 and no bonus > points will end up with a dynamic priority of MAX_PRIO - 1. > > Although the fact that niceness is primarily implemented by time slice > size means that this will have little or no adverse effect on the long > term allocation of CPU resources due to niceness, it could adversely > effect latency as it will interfere with preemption. > > The solution: > > Increase the number of priority slots in the run queues to allow a > linear mapping and eliminate the squish. > > The implementation: > > As the only place MAX_PRIO is used outside of sched.c is to initialize > the init task in init_task.h, it is possible to implement the solution > entirely within sched.c by defining a new macro IDLE_PRIO (which is > equal to the sum of MAX_PRIO and MAX_BONUS) and then replacing MAX_PRIO > by IDLE_PRIO where appropriate. > > Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
I overlooked the effect of this patch on the TASK_INTERACTIVE() macro function and this has an adverse effect on interactive responsiveness. A modified patch that corrects that oversight is attached.
Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
sched.c | 38 ++++++++++++++++++-------------------- 1 files changed, 18 insertions(+), 20 deletions(-)
-- Peter Williams pwil3058@bigpond.net.au
"Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce Index: GIT-warnings/kernel/sched.c =================================================================== --- GIT-warnings.orig/kernel/sched.c 2005-12-21 15:11:09.000000000 +1100 +++ GIT-warnings/kernel/sched.c 2005-12-21 15:54:49.000000000 +1100 @@ -145,7 +145,7 @@ (SCALE(TASK_NICE(p), 40, MAX_BONUS) + INTERACTIVE_DELTA) #define TASK_INTERACTIVE(p) \ - ((p)->prio <= (p)->static_prio - DELTA(p)) + ((p)->prio <= (p)->static_prio - DELTA(p) + MAX_BONUS / 2) #define INTERACTIVE_SLEEP(p) \ (JIFFIES_TO_NS(MAX_SLEEP_AVG * \ @@ -180,14 +180,15 @@ static unsigned int task_timeslice(task_ * These are the runqueue data structures: */ -#define BITMAP_SIZE ((((MAX_PRIO+1+7)/8)+sizeof(long)-1)/sizeof(long)) +#define IDLE_PRIO (MAX_PRIO + MAX_BONUS) +#define BITMAP_SIZE ((((IDLE_PRIO+1+7)/8)+sizeof(long)-1)/sizeof(long)) typedef struct runqueue runqueue_t; struct prio_array { unsigned int nr_active; unsigned long bitmap[BITMAP_SIZE]; - struct list_head queue[MAX_PRIO]; + struct list_head queue[IDLE_PRIO]; }; /* @@ -645,18 +646,15 @@ static inline void enqueue_task_head(str */ static int effective_prio(task_t *p) { - int bonus, prio; + int prio; if (rt_task(p)) return p->prio; - bonus = CURRENT_BONUS(p) - MAX_BONUS / 2; + prio = p->static_prio + MAX_BONUS - CURRENT_BONUS(p); + BUG_ON(prio < MAX_RT_PRIO); + BUG_ON(prio > IDLE_PRIO - 1); - prio = p->static_prio - bonus; - if (prio < MAX_RT_PRIO) - prio = MAX_RT_PRIO; - if (prio > MAX_PRIO-1) - prio = MAX_PRIO-1; return prio; } @@ -1861,7 +1859,7 @@ void pull_task(runqueue_t *src_rq, prio_ p->timestamp = (p->timestamp - src_rq->timestamp_last_tick) + this_rq->timestamp_last_tick; /* - * Note that idle threads have a prio of MAX_PRIO, for this test + * Note that idle threads have a prio of IDLE_PRIO, for this test * to be always true for them. */ if (TASK_PREEMPTS_CURR(p, this_rq)) @@ -1945,8 +1943,8 @@ skip_bitmap: if (!idx) idx = sched_find_first_bit(array->bitmap); else - idx = find_next_bit(array->bitmap, MAX_PRIO, idx); - if (idx >= MAX_PRIO) { + idx = find_next_bit(array->bitmap, IDLE_PRIO, idx); + if (idx >= IDLE_PRIO) { if (array == busiest->expired && busiest->active->nr_active) { array = busiest->active; dst_array = this_rq->active; @@ -3056,7 +3054,7 @@ go_idle: rq->expired = array; array = rq->active; rq->expired_timestamp = 0; - rq->best_expired_prio = MAX_PRIO; + rq->best_expired_prio = IDLE_PRIO; } idx = sched_find_first_bit(array->bitmap); @@ -4396,7 +4394,7 @@ void __devinit init_idle(task_t *idle, i idle->sleep_avg = 0; idle->array = NULL; - idle->prio = MAX_PRIO; + idle->prio = IDLE_PRIO; idle->state = TASK_RUNNING; idle->cpus_allowed = cpumask_of_cpu(cpu); set_task_cpu(idle, cpu); @@ -4737,7 +4735,7 @@ static void migrate_dead_tasks(unsigned struct runqueue *rq = cpu_rq(dead_cpu); for (arr = 0; arr < 2; arr++) { - for (i = 0; i < MAX_PRIO; i++) { + for (i = 0; i < IDLE_PRIO; i++) { struct list_head *list = &rq->arrays[arr].queue[i]; while (!list_empty(list)) migrate_dead(dead_cpu, @@ -4793,7 +4791,7 @@ static int migration_call(struct notifie /* Idle task back to normal (off runqueue, low prio) */ rq = task_rq_lock(rq->idle, &flags); deactivate_task(rq->idle, rq); - rq->idle->static_prio = MAX_PRIO; + rq->idle->static_prio = IDLE_PRIO; __setscheduler(rq->idle, SCHED_NORMAL, 0); migrate_dead_tasks(cpu); task_rq_unlock(rq, &flags); @@ -5610,7 +5608,7 @@ void __init sched_init(void) rq->nr_running = 0; rq->active = rq->arrays; rq->expired = rq->arrays + 1; - rq->best_expired_prio = MAX_PRIO; + rq->best_expired_prio = IDLE_PRIO; #ifdef CONFIG_SMP rq->sd = NULL; @@ -5625,12 +5623,12 @@ void __init sched_init(void) for (j = 0; j < 2; j++) { array = rq->arrays + j; - for (k = 0; k < MAX_PRIO; k++) { + for (k = 0; k < IDLE_PRIO; k++) { INIT_LIST_HEAD(array->queue + k); __clear_bit(k, array->bitmap); } // delimiter for bitsearch - __set_bit(MAX_PRIO, array->bitmap); + __set_bit(IDLE_PRIO, array->bitmap); } } | |