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Subject[RFC PATCH 2/5] sched: Add NOHZ_STATS_KICK

Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/core.c | 4 +--
kernel/sched/fair.c | 52 ++++++++++++++++++++++++++++++++++-----------------
kernel/sched/sched.h | 4 +++
3 files changed, 41 insertions(+), 19 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -608,7 +608,7 @@ static inline bool got_nohz_idle_kick(vo
{
int cpu = smp_processor_id();

- if (!(atomic_read(nohz_flags(cpu)) & NOHZ_BALANCE_KICK))
+ if (!(atomic_read(nohz_flags(cpu)) & NOHZ_KICK_MASK))
return false;

if (idle_cpu(cpu) && !need_resched())
@@ -618,7 +618,7 @@ static inline bool got_nohz_idle_kick(vo
* We can't run Idle Load Balance on this CPU for this time so we
* cancel it and clear NOHZ_BALANCE_KICK
*/
- atomic_andnot(NOHZ_BALANCE_KICK, nohz_flags(cpu));
+ atomic_andnot(NOHZ_KICK_MASK, nohz_flags(cpu));
return false;
}

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9001,8 +9001,8 @@ static void nohz_balancer_kick(void)
if (ilb_cpu >= nr_cpu_ids)
return;

- flags = atomic_fetch_or(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu));
- if (flags & NOHZ_BALANCE_KICK)
+ flags = atomic_fetch_or(NOHZ_KICK_MASK, nohz_flags(ilb_cpu));
+ if (flags & NOHZ_KICK_MASK)
return;
/*
* Use smp_send_reschedule() instead of resched_cpu().
@@ -9125,8 +9125,6 @@ static void rebalance_domains(struct rq
int need_serialize, need_decay = 0;
u64 max_cost = 0;

- update_blocked_averages(cpu);
-
rcu_read_lock();
for_each_domain(cpu, sd) {
/*
@@ -9221,20 +9219,27 @@ static void rebalance_domains(struct rq
* In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
* rebalancing for all the cpus for whom scheduler ticks are stopped.
*/
-static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
+static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
{
- int this_cpu = this_rq->cpu;
- struct rq *rq;
- int balance_cpu;
/* Earliest time when we have to do rebalance again */
unsigned long next_balance = jiffies + 60*HZ;
int update_next_balance = 0;
+ int this_cpu = this_rq->cpu;
+ unsigned int flags;
+ int balance_cpu;
+ struct rq *rq;

- if (!(atomic_read(nohz_flags(this_cpu)) & NOHZ_BALANCE_KICK))
- return;
+ if (!(atomic_read(nohz_flags(this_cpu)) & NOHZ_KICK_MASK))
+ return false;

- if (idle != CPU_IDLE)
- goto end;
+ if (idle != CPU_IDLE) {
+ atomic_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
+ return false;
+ }
+
+ flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
+
+ SCHED_WARN_ON((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);

for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
@@ -9262,7 +9267,9 @@ static void nohz_idle_balance(struct rq
cpu_load_update_idle(rq);
rq_unlock_irq(rq, &rf);

- rebalance_domains(rq, CPU_IDLE);
+ update_blocked_averages(rq->cpu);
+ if (flags & NOHZ_BALANCE_KICK)
+ rebalance_domains(rq, CPU_IDLE);
}

if (time_after(next_balance, rq->next_balance)) {
@@ -9271,6 +9278,10 @@ static void nohz_idle_balance(struct rq
}
}

+ update_blocked_averages(this_cpu);
+ if (flags & NOHZ_BALANCE_KICK)
+ rebalance_domains(this_rq, CPU_IDLE);
+
/*
* 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
@@ -9278,8 +9289,8 @@ static void nohz_idle_balance(struct rq
*/
if (likely(update_next_balance))
nohz.next_balance = next_balance;
-end:
- atomic_andnot(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
+
+ return true;
}

/*
@@ -9366,7 +9377,10 @@ static inline bool nohz_kick_needed(stru
return kick;
}
#else
-static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
+static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
+{
+ return false;
+}
#endif

/*
@@ -9387,7 +9401,11 @@ static __latent_entropy void run_rebalan
* load balance only within the local sched_domain hierarchy
* and abort nohz_idle_balance altogether if we pull some load.
*/
- nohz_idle_balance(this_rq, idle);
+ if (nohz_idle_balance(this_rq, idle))
+ return;
+
+ /* normal load balance */
+ update_blocked_averages(this_rq->cpu);
rebalance_domains(this_rq, idle);
}

--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2005,9 +2005,13 @@ extern void cfs_bandwidth_usage_dec(void
#ifdef CONFIG_NO_HZ_COMMON
#define NOHZ_TICK_STOPPED_BIT 0
#define NOHZ_BALANCE_KICK_BIT 1
+#define NOHZ_STATS_KICK_BIT 2

#define NOHZ_TICK_STOPPED BIT(NOHZ_TICK_STOPPED_BIT)
#define NOHZ_BALANCE_KICK BIT(NOHZ_BALANCE_KICK_BIT)
+#define NOHZ_STATS_KICK BIT(NOHZ_STATS_KICK_BIT)
+
+#define NOHZ_KICK_MASK (NOHZ_BALANCE_KICK | NOHZ_STATS_KICK)

#define nohz_flags(cpu) (&cpu_rq(cpu)->nohz_flags)


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