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Subject[patch 1/6] sched, nohz: introduce nohz_flags in the struct rq
Introduce nohz_flags in the struct rq, which will track two flags for now.

NOHZ_TICK_STOPPED will convey the stop tick status that gets set when
the tick is stopped and cleared during the first busy tick after the tick
is restarted.

NOHZ_BALANCE_KICK will track the need for nohz idle load balance
on this rq.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
kernel/sched/core.c | 5 +++--
kernel/sched/fair.c | 40 +++++++++++++++++++++-------------------
kernel/sched/sched.h | 10 +++++++++-
3 files changed, 33 insertions(+), 22 deletions(-)
Index: tip/kernel/sched/core.c
===================================================================
--- tip.orig/kernel/sched/core.c
+++ tip/kernel/sched/core.c
@@ -575,7 +575,8 @@ void wake_up_idle_cpu(int cpu)

static inline bool got_nohz_idle_kick(void)
{
- return idle_cpu(smp_processor_id()) && this_rq()->nohz_balance_kick;
+ int cpu = smp_processor_id();
+ return idle_cpu(cpu) && test_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu));
}

#else /* CONFIG_NO_HZ */
@@ -6833,7 +6834,7 @@ void __init sched_init(void)
rq->avg_idle = 2*sysctl_sched_migration_cost;
rq_attach_root(rq, &def_root_domain);
#ifdef CONFIG_NO_HZ
- rq->nohz_balance_kick = 0;
+ rq->nohz_flags = 0;
#endif
#endif
init_rq_hrtick(rq);
Index: tip/kernel/sched/fair.c
===================================================================
--- tip.orig/kernel/sched/fair.c
+++ tip/kernel/sched/fair.c
@@ -4866,18 +4866,15 @@ static void nohz_balancer_kick(int cpu)
return;
}

- if (!cpu_rq(ilb_cpu)->nohz_balance_kick) {
- cpu_rq(ilb_cpu)->nohz_balance_kick = 1;
-
- smp_mb();
- /*
- * Use smp_send_reschedule() instead of resched_cpu().
- * This way we generate a sched IPI on the target cpu which
- * is idle. And the softirq performing nohz idle load balance
- * will be run before returning from the IPI.
- */
- smp_send_reschedule(ilb_cpu);
- }
+ if (test_and_set_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu)))
+ return;
+ /*
+ * Use smp_send_reschedule() instead of resched_cpu().
+ * This way we generate a sched IPI on the target cpu which
+ * is idle. And the softirq performing nohz idle load balance
+ * will be run before returning from the IPI.
+ */
+ smp_send_reschedule(ilb_cpu);
return;
}

@@ -4941,6 +4938,8 @@ void select_nohz_load_balancer(int stop_
}
return;
}
+
+ set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
} else {
if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
return;
@@ -5056,8 +5055,9 @@ static void nohz_idle_balance(int this_c
struct rq *rq;
int balance_cpu;

- if (idle != CPU_IDLE || !this_rq->nohz_balance_kick)
- return;
+ if (idle != CPU_IDLE ||
+ !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
+ goto end;

for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
if (balance_cpu == this_cpu)
@@ -5068,10 +5068,8 @@ static void nohz_idle_balance(int this_c
* work being done for other cpus. Next load
* balancing owner will pick it up.
*/
- if (need_resched()) {
- this_rq->nohz_balance_kick = 0;
+ if (need_resched())
break;
- }

raw_spin_lock_irq(&this_rq->lock);
update_rq_clock(this_rq);
@@ -5085,7 +5083,8 @@ static void nohz_idle_balance(int this_c
this_rq->next_balance = rq->next_balance;
}
nohz.next_balance = this_rq->next_balance;
- this_rq->nohz_balance_kick = 0;
+end:
+ clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
}

/*
@@ -5106,6 +5105,9 @@ static inline int nohz_kick_needed(struc
int ret;
int first_pick_cpu, second_pick_cpu;

+ if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu))))
+ clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
+
if (time_before(now, nohz.next_balance))
return 0;

@@ -5173,7 +5175,7 @@ void trigger_load_balance(struct rq *rq,
likely(!on_null_domain(cpu)))
raise_softirq(SCHED_SOFTIRQ);
#ifdef CONFIG_NO_HZ
- else if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
+ if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
nohz_balancer_kick(cpu);
#endif
}
Index: tip/kernel/sched/sched.h
===================================================================
--- tip.orig/kernel/sched/sched.h
+++ tip/kernel/sched/sched.h
@@ -371,7 +371,7 @@ struct rq {
unsigned long last_load_update_tick;
#ifdef CONFIG_NO_HZ
u64 nohz_stamp;
- unsigned char nohz_balance_kick;
+ unsigned long nohz_flags;
#endif
int skip_clock_update;

@@ -1062,3 +1062,11 @@ extern void init_rt_rq(struct rt_rq *rt_
extern void unthrottle_offline_cfs_rqs(struct rq *rq);

extern void account_cfs_bandwidth_used(int enabled, int was_enabled);
+
+#ifdef CONFIG_NO_HZ
+enum rq_nohz_flag_bits {
+ NOHZ_TICK_STOPPED,
+ NOHZ_BALANCE_KICK,
+};
+#define nohz_flags(cpu) (&cpu_rq(cpu)->nohz_flags)
+#endif /* CONFIG_NO_HZ */



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