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Subject[RFC PATCH 1/5] sched: Convert nohz_flags to atomic_t


Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/core.c | 6 +++---
kernel/sched/fair.c | 23 +++++++++++++++--------
kernel/sched/sched.h | 11 ++++++-----
3 files changed, 24 insertions(+), 16 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 (!test_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu)))
+ if (!(atomic_read(nohz_flags(cpu)) & NOHZ_BALANCE_KICK))
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
*/
- clear_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu));
+ atomic_andnot(NOHZ_BALANCE_KICK, nohz_flags(cpu));
return false;
}

@@ -6002,7 +6002,7 @@ void __init sched_init(void)
rq_attach_root(rq, &def_root_domain);
#ifdef CONFIG_NO_HZ_COMMON
rq->last_load_update_tick = jiffies;
- rq->nohz_flags = 0;
+ atomic_set(&rq->nohz_flags, 0);
#endif
#ifdef CONFIG_NO_HZ_FULL
rq->last_sched_tick = 0;
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8991,6 +8991,7 @@ static inline int find_new_ilb(void)
*/
static void nohz_balancer_kick(void)
{
+ unsigned int flags;
int ilb_cpu;

nohz.next_balance++;
@@ -9000,7 +9001,8 @@ static void nohz_balancer_kick(void)
if (ilb_cpu >= nr_cpu_ids)
return;

- if (test_and_set_bit(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu)))
+ flags = atomic_fetch_or(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu));
+ if (flags & NOHZ_BALANCE_KICK)
return;
/*
* Use smp_send_reschedule() instead of resched_cpu().
@@ -9014,7 +9016,9 @@ static void nohz_balancer_kick(void)

void nohz_balance_exit_idle(unsigned int cpu)
{
- if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
+ unsigned int flags = atomic_read(nohz_flags(cpu));
+
+ if (unlikely(flags & NOHZ_TICK_STOPPED)) {
/*
* Completely isolated CPUs don't ever set, so we must test.
*/
@@ -9022,7 +9026,8 @@ void nohz_balance_exit_idle(unsigned int
cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
atomic_dec(&nohz.nr_cpus);
}
- clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
+
+ atomic_andnot(NOHZ_TICK_STOPPED, nohz_flags(cpu));
}
}

@@ -9076,7 +9081,7 @@ void nohz_balance_enter_idle(int cpu)
if (!housekeeping_cpu(cpu, HK_FLAG_SCHED))
return;

- if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
+ if (atomic_read(nohz_flags(cpu)) & NOHZ_TICK_STOPPED)
return;

/*
@@ -9087,7 +9092,7 @@ void nohz_balance_enter_idle(int cpu)

cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
atomic_inc(&nohz.nr_cpus);
- set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
+ atomic_or(NOHZ_TICK_STOPPED, nohz_flags(cpu));
}
#endif

@@ -9225,8 +9230,10 @@ static void nohz_idle_balance(struct rq
unsigned long next_balance = jiffies + 60*HZ;
int update_next_balance = 0;

- if (idle != CPU_IDLE ||
- !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
+ if (!(atomic_read(nohz_flags(this_cpu)) & NOHZ_BALANCE_KICK))
+ return;
+
+ if (idle != CPU_IDLE)
goto end;

for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
@@ -9272,7 +9279,7 @@ static void nohz_idle_balance(struct rq
if (likely(update_next_balance))
nohz.next_balance = next_balance;
end:
- clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
+ atomic_andnot(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
}

/*
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -723,7 +723,7 @@ struct rq {
#ifdef CONFIG_SMP
unsigned long last_load_update_tick;
#endif /* CONFIG_SMP */
- unsigned long nohz_flags;
+ atomic_t nohz_flags;
#endif /* CONFIG_NO_HZ_COMMON */
#ifdef CONFIG_NO_HZ_FULL
unsigned long last_sched_tick;
@@ -2003,10 +2003,11 @@ extern void cfs_bandwidth_usage_inc(void
extern void cfs_bandwidth_usage_dec(void);

#ifdef CONFIG_NO_HZ_COMMON
-enum rq_nohz_flag_bits {
- NOHZ_TICK_STOPPED,
- NOHZ_BALANCE_KICK,
-};
+#define NOHZ_TICK_STOPPED_BIT 0
+#define NOHZ_BALANCE_KICK_BIT 1
+
+#define NOHZ_TICK_STOPPED BIT(NOHZ_TICK_STOPPED_BIT)
+#define NOHZ_BALANCE_KICK BIT(NOHZ_BALANCE_KICK_BIT)

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


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