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Subject[RFC PATCH 4/5] sched: Add nohz stats balancing

Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/fair.c | 31 +++++++++++++++++++------------
1 file changed, 19 insertions(+), 12 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8972,6 +8972,7 @@ static struct {
cpumask_var_t idle_cpus_mask;
atomic_t nr_cpus;
unsigned long next_balance; /* in jiffy units */
+ unsigned long next_stats;
} nohz ____cacheline_aligned;

static inline int find_new_ilb(void)
@@ -9006,9 +9007,8 @@ static inline void set_cpu_sd_state_busy
* nohz_load_balancer CPU (if there is one) otherwise fallback to any idle
* CPU (if there is one).
*/
-static void kick_ilb(void)
+static void kick_ilb(unsigned int flags)
{
- unsigned int flags;
int ilb_cpu;

nohz.next_balance++;
@@ -9018,7 +9018,7 @@ static void kick_ilb(void)
if (ilb_cpu >= nr_cpu_ids)
return;

- flags = atomic_fetch_or(NOHZ_KICK_MASK, nohz_flags(ilb_cpu));
+ flags = atomic_fetch_or(flags, nohz_flags(ilb_cpu));
if (flags & NOHZ_KICK_MASK)
return;

@@ -9048,7 +9048,7 @@ static void nohz_balancer_kick(struct rq
struct sched_domain_shared *sds;
struct sched_domain *sd;
int nr_busy, i, cpu = rq->cpu;
- bool kick = false;
+ unsigned int flags = 0;

if (unlikely(rq->idle_balance))
return;
@@ -9067,11 +9067,14 @@ static void nohz_balancer_kick(struct rq
if (likely(!atomic_read(&nohz.nr_cpus)))
return;

+ if (time_after(now, nohz.next_stats))
+ flags = NOHZ_STATS_KICK;
+
if (time_before(now, nohz.next_balance))
- return;
+ goto out;

if (rq->nr_running >= 2) {
- kick = true;
+ flags = NOHZ_KICK_MASK;
goto out;
}

@@ -9084,7 +9087,7 @@ static void nohz_balancer_kick(struct rq
*/
nr_busy = atomic_read(&sds->nr_busy_cpus);
if (nr_busy > 1) {
- kick = true;
+ flags = NOHZ_KICK_MASK
goto unlock;
}

@@ -9094,7 +9097,7 @@ static void nohz_balancer_kick(struct rq
if (sd) {
if ((rq->cfs.h_nr_running >= 1) &&
check_cpu_capacity(rq, sd)) {
- kick = true;
+ flags = NOHZ_KICK_MASK;
goto unlock;
}
}
@@ -9107,7 +9110,7 @@ static void nohz_balancer_kick(struct rq
continue;

if (sched_asym_prefer(i, cpu)) {
- kick = true;
+ flags = NOHZ_KICK_MASK;
goto unlock;
}
}
@@ -9115,8 +9118,8 @@ static void nohz_balancer_kick(struct rq
unlock:
rcu_read_unlock();
out:
- if (kick)
- kick_ilb();
+ if (flags)
+ kick_ilb(flags);
}

void nohz_balance_exit_idle(unsigned int cpu)
@@ -9312,7 +9315,9 @@ static void rebalance_domains(struct rq
static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
{
/* Earliest time when we have to do rebalance again */
- unsigned long next_balance = jiffies + 60*HZ;
+ unsigned long now = jiffies;
+ unsigned long next_balance = now + 60*HZ;
+ unsigned long next_stats = now + msecs_to_jiffies(LOAD_AVG_PERIOD);
int update_next_balance = 0;
int this_cpu = this_rq->cpu;
unsigned int flags;
@@ -9372,6 +9377,8 @@ static bool nohz_idle_balance(struct rq
if (flags & NOHZ_BALANCE_KICK)
rebalance_domains(this_rq, CPU_IDLE);

+ nohz.next_stats = next_stats;
+
/*
* next_balance will be updated only when there is a need.
* When the CPU is attached to null domain for ex, it will not be

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