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sched/fair: Wait before decaying max_newidle_lb_cost

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Decay max_newidle_lb_cost only when it has not been updated for a while
and ensure to not decay a recently changed value.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20211019123537.17146-4-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2021-10-19 14:35:35 +02:00 committed by Peter Zijlstra
parent 9d783c8dd1
commit e60b56e46b
3 changed files with 29 additions and 11 deletions
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2
include/linux/sched/topology.h
View File

@ -105,7 +105,7 @@ struct sched_domain {
/* idle_balance() stats */
u64 max_newidle_lb_cost;
unsigned long next_decay_max_lb_cost;
unsigned long last_decay_max_lb_cost;
u64 avg_scan_cost; /* select_idle_sibling */

36
kernel/sched/fair.c
View File

@ -10239,6 +10239,30 @@ void update_max_interval(void)
max_load_balance_interval = HZ*num_online_cpus()/10;
}
static inline bool update_newidle_cost(struct sched_domain *sd, u64 cost)
{
if (cost > sd->max_newidle_lb_cost) {
/*
* Track max cost of a domain to make sure to not delay the
* next wakeup on the CPU.
*/
sd->max_newidle_lb_cost = cost;
sd->last_decay_max_lb_cost = jiffies;
} else if (time_after(jiffies, sd->last_decay_max_lb_cost + HZ)) {
/*
* Decay the newidle max times by ~1% per second to ensure that
* it is not outdated and the current max cost is actually
* shorter.
*/
sd->max_newidle_lb_cost = (sd->max_newidle_lb_cost * 253) / 256;
sd->last_decay_max_lb_cost = jiffies;
return true;
}
return false;
}
/*
* It checks each scheduling domain to see if it is due to be balanced,
* and initiates a balancing operation if so.
@ -10262,14 +10286,9 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
for_each_domain(cpu, sd) {
/*
* Decay the newidle max times here because this is a regular
* visit to all the domains. Decay ~1% per second.
* visit to all the domains.
*/
if (time_after(jiffies, sd->next_decay_max_lb_cost)) {
sd->max_newidle_lb_cost =
(sd->max_newidle_lb_cost * 253) / 256;
sd->next_decay_max_lb_cost = jiffies + HZ;
need_decay = 1;
}
need_decay = update_newidle_cost(sd, 0);
max_cost += sd->max_newidle_lb_cost;
/*
@ -10911,8 +10930,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
t1 = sched_clock_cpu(this_cpu);
domain_cost = t1 - t0;
if (domain_cost > sd->max_newidle_lb_cost)
sd->max_newidle_lb_cost = domain_cost;
update_newidle_cost(sd, domain_cost);
curr_cost += domain_cost;
t0 = t1;

2
kernel/sched/topology.c
View File

@ -1568,7 +1568,7 @@ sd_init(struct sched_domain_topology_level *tl,
.last_balance = jiffies,
.balance_interval = sd_weight,
.max_newidle_lb_cost = 0,
.next_decay_max_lb_cost = jiffies,
.last_decay_max_lb_cost = jiffies,
.child = child,
#ifdef CONFIG_SCHED_DEBUG
.name = tl->name,