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sched/fair: Commit to EEVDF 

EEVDF is a better defined scheduling policy, as a result it has less
heuristics/tunables. There is no compelling reason to keep CFS around.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230531124604.137187212@infradead.org
This commit is contained in:
Peter Zijlstra 2023-05-31 13:58:47 +02:00 committed by Ingo Molnar
parent e8f331bcc2
commit 5e963f2bd4
4 changed files with 38 additions and 450 deletions
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6
kernel/sched/debug.c
View File

@ -347,10 +347,7 @@ static __init int sched_init_debug(void)
debugfs_create_file("preempt", 0644, debugfs_sched, NULL, &sched_dynamic_fops);
#endif
debugfs_create_u32("latency_ns", 0644, debugfs_sched, &sysctl_sched_latency);
debugfs_create_u32("min_granularity_ns", 0644, debugfs_sched, &sysctl_sched_min_granularity);
debugfs_create_u32("idle_min_granularity_ns", 0644, debugfs_sched, &sysctl_sched_idle_min_granularity);
debugfs_create_u32("wakeup_granularity_ns", 0644, debugfs_sched, &sysctl_sched_wakeup_granularity);
debugfs_create_u32("latency_warn_ms", 0644, debugfs_sched, &sysctl_resched_latency_warn_ms);
debugfs_create_u32("latency_warn_once", 0644, debugfs_sched, &sysctl_resched_latency_warn_once);
@ -866,10 +863,7 @@ static void sched_debug_header(struct seq_file *m)
SEQ_printf(m, " .%-40s: %Ld\n", #x, (long long)(x))
#define PN(x) \
SEQ_printf(m, " .%-40s: %Ld.%06ld\n", #x, SPLIT_NS(x))
PN(sysctl_sched_latency);
PN(sysctl_sched_min_granularity);
PN(sysctl_sched_idle_min_granularity);
PN(sysctl_sched_wakeup_granularity);
P(sysctl_sched_child_runs_first);
P(sysctl_sched_features);
#undef PN

465
kernel/sched/fair.c
View File

@ -57,22 +57,6 @@
#include "stats.h"
#include "autogroup.h"
/*
* Targeted preemption latency for CPU-bound tasks:
*
* NOTE: this latency value is not the same as the concept of
* 'timeslice length' - timeslices in CFS are of variable length
* and have no persistent notion like in traditional, time-slice
* based scheduling concepts.
*
* (to see the precise effective timeslice length of your workload,
* run vmstat and monitor the context-switches (cs) field)
*
* (default: 6ms * (1 + ilog(ncpus)), units: nanoseconds)
*/
unsigned int sysctl_sched_latency = 6000000ULL;
static unsigned int normalized_sysctl_sched_latency = 6000000ULL;
/*
* The initial- and re-scaling of tunables is configurable
*
@ -94,37 +78,12 @@ unsigned int sysctl_sched_tunable_scaling = SCHED_TUNABLESCALING_LOG;
unsigned int sysctl_sched_min_granularity = 750000ULL;
static unsigned int normalized_sysctl_sched_min_granularity = 750000ULL;
/*
* Minimal preemption granularity for CPU-bound SCHED_IDLE tasks.
* Applies only when SCHED_IDLE tasks compete with normal tasks.
*
* (default: 0.75 msec)
*/
unsigned int sysctl_sched_idle_min_granularity = 750000ULL;
/*
* This value is kept at sysctl_sched_latency/sysctl_sched_min_granularity
*/
static unsigned int sched_nr_latency = 8;
/*
* After fork, child runs first. If set to 0 (default) then
* parent will (try to) run first.
*/
unsigned int sysctl_sched_child_runs_first __read_mostly;
/*
* SCHED_OTHER wake-up granularity.
*
* This option delays the preemption effects of decoupled workloads
* and reduces their over-scheduling. Synchronous workloads will still
* have immediate wakeup/sleep latencies.
*
* (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
*/
unsigned int sysctl_sched_wakeup_granularity = 1000000UL;
static unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL;
const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
int sched_thermal_decay_shift;
@ -279,8 +238,6 @@ static void update_sysctl(void)
#define SET_SYSCTL(name) \
(sysctl_##name = (factor) * normalized_sysctl_##name)
SET_SYSCTL(sched_min_granularity);
SET_SYSCTL(sched_latency);
SET_SYSCTL(sched_wakeup_granularity);
#undef SET_SYSCTL
}
@ -888,30 +845,6 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
return __node_2_se(left);
}
static struct sched_entity *__pick_next_entity(struct sched_entity *se)
{
struct rb_node *next = rb_next(&se->run_node);
if (!next)
return NULL;
return __node_2_se(next);
}
static struct sched_entity *pick_cfs(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
struct sched_entity *left = __pick_first_entity(cfs_rq);
/*
* If curr is set we have to see if its left of the leftmost entity
* still in the tree, provided there was anything in the tree at all.
*/
if (!left || (curr && entity_before(curr, left)))
left = curr;
return left;
}
/*
* Earliest Eligible Virtual Deadline First
*
@ -1008,85 +941,15 @@ int sched_update_scaling(void)
{
unsigned int factor = get_update_sysctl_factor();
sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
sysctl_sched_min_granularity);
#define WRT_SYSCTL(name) \
(normalized_sysctl_##name = sysctl_##name / (factor))
WRT_SYSCTL(sched_min_granularity);
WRT_SYSCTL(sched_latency);
WRT_SYSCTL(sched_wakeup_granularity);
#undef WRT_SYSCTL
return 0;
}
#endif
/*
* The idea is to set a period in which each task runs once.
*
* When there are too many tasks (sched_nr_latency) we have to stretch
* this period because otherwise the slices get too small.
*
* p = (nr <= nl) ? l : l*nr/nl
*/
static u64 __sched_period(unsigned long nr_running)
{
if (unlikely(nr_running > sched_nr_latency))
return nr_running * sysctl_sched_min_granularity;
else
return sysctl_sched_latency;
}
static bool sched_idle_cfs_rq(struct cfs_rq *cfs_rq);
/*
* We calculate the wall-time slice from the period by taking a part
* proportional to the weight.
*
* s = p*P[w/rw]
*/
static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
unsigned int nr_running = cfs_rq->nr_running;
struct sched_entity *init_se = se;
unsigned int min_gran;
u64 slice;
if (sched_feat(ALT_PERIOD))
nr_running = rq_of(cfs_rq)->cfs.h_nr_running;
slice = __sched_period(nr_running + !se->on_rq);
for_each_sched_entity(se) {
struct load_weight *load;
struct load_weight lw;
struct cfs_rq *qcfs_rq;
qcfs_rq = cfs_rq_of(se);
load = &qcfs_rq->load;
if (unlikely(!se->on_rq)) {
lw = qcfs_rq->load;
update_load_add(&lw, se->load.weight);
load = &lw;
}
slice = __calc_delta(slice, se->load.weight, load);
}
if (sched_feat(BASE_SLICE)) {
if (se_is_idle(init_se) && !sched_idle_cfs_rq(cfs_rq))
min_gran = sysctl_sched_idle_min_granularity;
else
min_gran = sysctl_sched_min_granularity;
slice = max_t(u64, slice, min_gran);
}
return slice;
}
static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se);
/*
@ -1098,35 +961,25 @@ static void update_deadline(struct cfs_rq *cfs_rq, struct sched_entity *se)
if ((s64)(se->vruntime - se->deadline) < 0)
return;
if (sched_feat(EEVDF)) {
/*
* For EEVDF the virtual time slope is determined by w_i (iow.
* nice) while the request time r_i is determined by
* sysctl_sched_min_granularity.
*/
se->slice = sysctl_sched_min_granularity;
/*
* The task has consumed its request, reschedule.
*/
if (cfs_rq->nr_running > 1) {
resched_curr(rq_of(cfs_rq));
clear_buddies(cfs_rq, se);
}
} else {
/*
* When many tasks blow up the sched_period; it is possible
* that sched_slice() reports unusually large results (when
* many tasks are very light for example). Therefore impose a
* maximum.
*/
se->slice = min_t(u64, sched_slice(cfs_rq, se), sysctl_sched_latency);
}
/*
* For EEVDF the virtual time slope is determined by w_i (iow.
* nice) while the request time r_i is determined by
* sysctl_sched_min_granularity.
*/
se->slice = sysctl_sched_min_granularity;
/*
* EEVDF: vd_i = ve_i + r_i / w_i
*/
se->deadline = se->vruntime + calc_delta_fair(se->slice, se);
/*
* The task has consumed its request, reschedule.
*/
if (cfs_rq->nr_running > 1) {
resched_curr(rq_of(cfs_rq));
clear_buddies(cfs_rq, se);
}
}
#include "pelt.h"
@ -5055,19 +4908,6 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq) {}
#endif /* CONFIG_SMP */
static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
s64 d = se->vruntime - cfs_rq->min_vruntime;
if (d < 0)
d = -d;
if (d > 3*sysctl_sched_latency)
schedstat_inc(cfs_rq->nr_spread_over);
#endif
}
static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
@ -5219,7 +5059,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
check_schedstat_required();
update_stats_enqueue_fair(cfs_rq, se, flags);
check_spread(cfs_rq, se);
if (!curr)
__enqueue_entity(cfs_rq, se);
se->on_rq = 1;
@ -5241,17 +5080,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
}
}
static void __clear_buddies_last(struct sched_entity *se)
{
for_each_sched_entity(se) {
struct cfs_rq *cfs_rq = cfs_rq_of(se);
if (cfs_rq->last != se)
break;
cfs_rq->last = NULL;
}
}
static void __clear_buddies_next(struct sched_entity *se)
{
for_each_sched_entity(se) {
@ -5263,27 +5091,10 @@ static void __clear_buddies_next(struct sched_entity *se)
}
}
static void __clear_buddies_skip(struct sched_entity *se)
{
for_each_sched_entity(se) {
struct cfs_rq *cfs_rq = cfs_rq_of(se);
if (cfs_rq->skip != se)
break;
cfs_rq->skip = NULL;
}
}
static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
if (cfs_rq->last == se)
__clear_buddies_last(se);
if (cfs_rq->next == se)
__clear_buddies_next(se);
if (cfs_rq->skip == se)
__clear_buddies_skip(se);
}
static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
@ -5341,45 +5152,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
update_idle_cfs_rq_clock_pelt(cfs_rq);
}
/*
* Preempt the current task with a newly woken task if needed:
*/
static void
check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
unsigned long delta_exec;
struct sched_entity *se;
s64 delta;
delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
if (delta_exec > curr->slice) {
resched_curr(rq_of(cfs_rq));
/*
* The current task ran long enough, ensure it doesn't get
* re-elected due to buddy favours.
*/
clear_buddies(cfs_rq, curr);
return;
}
/*
* Ensure that a task that missed wakeup preemption by a
* narrow margin doesn't have to wait for a full slice.
* This also mitigates buddy induced latencies under load.
*/
if (delta_exec < sysctl_sched_min_granularity)
return;
se = __pick_first_entity(cfs_rq);
delta = curr->vruntime - se->vruntime;
if (delta < 0)
return;
if (delta > curr->slice)
resched_curr(rq_of(cfs_rq));
}
static void
set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
@ -5418,9 +5190,6 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
se->prev_sum_exec_runtime = se->sum_exec_runtime;
}
static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);
/*
* Pick the next process, keeping these things in mind, in this order:
* 1) keep things fair between processes/task groups
@ -5431,53 +5200,14 @@ wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);
static struct sched_entity *
pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
struct sched_entity *left, *se;
if (sched_feat(EEVDF)) {
/*
* Enabling NEXT_BUDDY will affect latency but not fairness.
*/
if (sched_feat(NEXT_BUDDY) &&
cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next))
return cfs_rq->next;
return pick_eevdf(cfs_rq);
}
se = left = pick_cfs(cfs_rq, curr);
/*
* Avoid running the skip buddy, if running something else can
* be done without getting too unfair.
* Enabling NEXT_BUDDY will affect latency but not fairness.
*/
if (cfs_rq->skip && cfs_rq->skip == se) {
struct sched_entity *second;
if (sched_feat(NEXT_BUDDY) &&
cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next))
return cfs_rq->next;
if (se == curr) {
second = __pick_first_entity(cfs_rq);
} else {
second = __pick_next_entity(se);
if (!second || (curr && entity_before(curr, second)))
second = curr;
}
if (second && wakeup_preempt_entity(second, left) < 1)
se = second;
}
if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) {
/*
* Someone really wants this to run. If it's not unfair, run it.
*/
se = cfs_rq->next;
} else if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) {
/*
* Prefer last buddy, try to return the CPU to a preempted task.
*/
se = cfs_rq->last;
}
return se;
return pick_eevdf(cfs_rq);
}
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);
@ -5494,8 +5224,6 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
/* throttle cfs_rqs exceeding runtime */
check_cfs_rq_runtime(cfs_rq);
check_spread(cfs_rq, prev);
if (prev->on_rq) {
update_stats_wait_start_fair(cfs_rq, prev);
/* Put 'current' back into the tree. */
@ -5536,9 +5264,6 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
hrtimer_active(&rq_of(cfs_rq)->hrtick_timer))
return;
#endif
if (!sched_feat(EEVDF) && cfs_rq->nr_running > 1)
check_preempt_tick(cfs_rq, curr);
}
@ -6610,8 +6335,7 @@ static void hrtick_update(struct rq *rq)
if (!hrtick_enabled_fair(rq) || curr->sched_class != &fair_sched_class)
return;
if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
hrtick_start_fair(rq, curr);
hrtick_start_fair(rq, curr);
}
#else /* !CONFIG_SCHED_HRTICK */
static inline void
@ -6652,17 +6376,6 @@ static int sched_idle_rq(struct rq *rq)
rq->nr_running);
}
/*
* Returns true if cfs_rq only has SCHED_IDLE entities enqueued. Note the use
* of idle_nr_running, which does not consider idle descendants of normal
* entities.
*/
static bool sched_idle_cfs_rq(struct cfs_rq *cfs_rq)
{
return cfs_rq->nr_running &&
cfs_rq->nr_running == cfs_rq->idle_nr_running;
}
#ifdef CONFIG_SMP
static int sched_idle_cpu(int cpu)
{
@ -8205,66 +7918,6 @@ balance_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
}
#endif /* CONFIG_SMP */
static unsigned long wakeup_gran(struct sched_entity *se)
{
unsigned long gran = sysctl_sched_wakeup_granularity;
/*
* Since its curr running now, convert the gran from real-time
* to virtual-time in his units.
*
* By using 'se' instead of 'curr' we penalize light tasks, so
* they get preempted easier. That is, if 'se' < 'curr' then
* the resulting gran will be larger, therefore penalizing the
* lighter, if otoh 'se' > 'curr' then the resulting gran will
* be smaller, again penalizing the lighter task.
*
* This is especially important for buddies when the leftmost
* task is higher priority than the buddy.
*/
return calc_delta_fair(gran, se);
}
/*
* Should 'se' preempt 'curr'.
*
* |s1
* |s2
* |s3
* g
* |<--->|c
*
* w(c, s1) = -1
* w(c, s2) = 0
* w(c, s3) = 1
*
*/
static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
{
s64 gran, vdiff = curr->vruntime - se->vruntime;
if (vdiff <= 0)
return -1;
gran = wakeup_gran(se);
if (vdiff > gran)
return 1;
return 0;
}
static void set_last_buddy(struct sched_entity *se)
{
for_each_sched_entity(se) {
if (SCHED_WARN_ON(!se->on_rq))
return;
if (se_is_idle(se))
return;
cfs_rq_of(se)->last = se;
}
}
static void set_next_buddy(struct sched_entity *se)
{
for_each_sched_entity(se) {
@ -8276,12 +7929,6 @@ static void set_next_buddy(struct sched_entity *se)
}
}
static void set_skip_buddy(struct sched_entity *se)
{
for_each_sched_entity(se)
cfs_rq_of(se)->skip = se;
}
/*
* Preempt the current task with a newly woken task if needed:
*/
@ -8290,7 +7937,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
struct task_struct *curr = rq->curr;
struct sched_entity *se = &curr->se, *pse = &p->se;
struct cfs_rq *cfs_rq = task_cfs_rq(curr);
int scale = cfs_rq->nr_running >= sched_nr_latency;
int next_buddy_marked = 0;
int cse_is_idle, pse_is_idle;
@ -8306,7 +7952,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
return;
if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {
if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK)) {
set_next_buddy(pse);
next_buddy_marked = 1;
}
@ -8354,44 +8000,16 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
cfs_rq = cfs_rq_of(se);
update_curr(cfs_rq);
if (sched_feat(EEVDF)) {
/*
* XXX pick_eevdf(cfs_rq) != se ?
*/
if (pick_eevdf(cfs_rq) == pse)
goto preempt;
return;
}
if (wakeup_preempt_entity(se, pse) == 1) {
/*
* Bias pick_next to pick the sched entity that is
* triggering this preemption.
*/
if (!next_buddy_marked)
set_next_buddy(pse);
/*
* XXX pick_eevdf(cfs_rq) != se ?
*/
if (pick_eevdf(cfs_rq) == pse)
goto preempt;
}
return;
preempt:
resched_curr(rq);
/*
* Only set the backward buddy when the current task is still
* on the rq. This can happen when a wakeup gets interleaved
* with schedule on the ->pre_schedule() or idle_balance()
* point, either of which can * drop the rq lock.
*
* Also, during early boot the idle thread is in the fair class,
* for obvious reasons its a bad idea to schedule back to it.
*/
if (unlikely(!se->on_rq || curr == rq->idle))
return;
if (sched_feat(LAST_BUDDY) && scale && entity_is_task(se))
set_last_buddy(se);
}
#ifdef CONFIG_SMP
@ -8592,8 +8210,6 @@ static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
/*
* sched_yield() is very simple
*
* The magic of dealing with the ->skip buddy is in pick_next_entity.
*/
static void yield_task_fair(struct rq *rq)
{
@ -8609,23 +8225,19 @@ static void yield_task_fair(struct rq *rq)
clear_buddies(cfs_rq, se);
if (sched_feat(EEVDF) || curr->policy != SCHED_BATCH) {
update_rq_clock(rq);
/*
* Update run-time statistics of the 'current'.
*/
update_curr(cfs_rq);
/*
* Tell update_rq_clock() that we've just updated,
* so we don't do microscopic update in schedule()
* and double the fastpath cost.
*/
rq_clock_skip_update(rq);
}
if (sched_feat(EEVDF))
se->deadline += calc_delta_fair(se->slice, se);
update_rq_clock(rq);
/*
* Update run-time statistics of the 'current'.
*/
update_curr(cfs_rq);
/*
* Tell update_rq_clock() that we've just updated,
* so we don't do microscopic update in schedule()
* and double the fastpath cost.
*/
rq_clock_skip_update(rq);
set_skip_buddy(se);
se->deadline += calc_delta_fair(se->slice, se);
}
static bool yield_to_task_fair(struct rq *rq, struct task_struct *p)
@ -8873,8 +8485,7 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
* Buddy candidates are cache hot:
*/
if (sched_feat(CACHE_HOT_BUDDY) && env->dst_rq->nr_running &&
(&p->se == cfs_rq_of(&p->se)->next ||
&p->se == cfs_rq_of(&p->se)->last))
(&p->se == cfs_rq_of(&p->se)->next))
return 1;
if (sysctl_sched_migration_cost == -1)

12
kernel/sched/features.h
View File

@ -14,13 +14,6 @@ SCHED_FEAT(PLACE_DEADLINE_INITIAL, true)
*/
SCHED_FEAT(NEXT_BUDDY, false)
/*
* Prefer to schedule the task that ran last (when we did
* wake-preempt) as that likely will touch the same data, increases
* cache locality.
*/
SCHED_FEAT(LAST_BUDDY, true)
/*
* Consider buddies to be cache hot, decreases the likeliness of a
* cache buddy being migrated away, increases cache locality.
@ -93,8 +86,3 @@ SCHED_FEAT(UTIL_EST, true)
SCHED_FEAT(UTIL_EST_FASTUP, true)
SCHED_FEAT(LATENCY_WARN, false)
SCHED_FEAT(ALT_PERIOD, true)
SCHED_FEAT(BASE_SLICE, true)
SCHED_FEAT(EEVDF, true)

5
kernel/sched/sched.h
View File

@ -570,8 +570,6 @@ struct cfs_rq {
*/
struct sched_entity *curr;
struct sched_entity *next;
struct sched_entity *last;
struct sched_entity *skip;
#ifdef CONFIG_SCHED_DEBUG
unsigned int nr_spread_over;
@ -2508,9 +2506,6 @@ extern const_debug unsigned int sysctl_sched_migration_cost;
extern unsigned int sysctl_sched_min_granularity;
#ifdef CONFIG_SCHED_DEBUG
extern unsigned int sysctl_sched_latency;
extern unsigned int sysctl_sched_idle_min_granularity;
extern unsigned int sysctl_sched_wakeup_granularity;
extern int sysctl_resched_latency_warn_ms;
extern int sysctl_resched_latency_warn_once;