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sched/nohz: Clean up nohz enter/exit

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The primary observation is that nohz enter/exit is always from the
current CPU, therefore NOHZ_TICK_STOPPED does not in fact need to be
an atomic.

Secondary is that we appear to have 2 nearly identical hooks in the
nohz enter code, set_cpu_sd_state_idle() and
nohz_balance_enter_idle(). Fold the whole set_cpu_sd_state thing into
nohz_balance_{enter,exit}_idle.

Removes an atomic op from both enter and exit paths.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2017-12-21 15:06:50 +01:00 committed by Ingo Molnar
parent e022e0d38a
commit 00357f5ec5
5 changed files with 48 additions and 57 deletions
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2
include/linux/sched/nohz.h
View file

@ -16,11 +16,9 @@ static inline void cpu_load_update_nohz_stop(void) { }
#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
extern void nohz_balance_enter_idle(int cpu);
extern void set_cpu_sd_state_idle(void);
extern int get_nohz_timer_target(void);
#else
static inline void nohz_balance_enter_idle(int cpu) { }
static inline void set_cpu_sd_state_idle(void) { }
#endif
#ifdef CONFIG_NO_HZ_COMMON

2
kernel/sched/core.c
View file

@ -5861,7 +5861,7 @@ int sched_cpu_dying(unsigned int cpu)
calc_load_migrate(rq);
update_max_interval();
nohz_balance_exit_idle(cpu);
nohz_balance_exit_idle(rq);
hrtick_clear(rq);
return 0;
}

83
kernel/sched/fair.c
View file

@ -9103,23 +9103,6 @@ static inline int find_new_ilb(void)
return nr_cpu_ids;
}
static inline void set_cpu_sd_state_busy(void)
{
struct sched_domain *sd;
int cpu = smp_processor_id();
rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_llc, cpu));
if (!sd || !sd->nohz_idle)
goto unlock;
sd->nohz_idle = 0;
atomic_inc(&sd->shared->nr_busy_cpus);
unlock:
rcu_read_unlock();
}
/*
* Kick a CPU to do the nohz balancing, if it is time for it. We pick the
* nohz_load_balancer CPU (if there is one) otherwise fallback to any idle
@ -9175,8 +9158,7 @@ static void nohz_balancer_kick(struct rq *rq)
* We may be recently in ticked or tickless idle mode. At the first
* busy tick after returning from idle, we will update the busy stats.
*/
set_cpu_sd_state_busy();
nohz_balance_exit_idle(cpu);
nohz_balance_exit_idle(rq);
/*
* None are in tickless mode and hence no need for NOHZ idle load
@ -9240,27 +9222,39 @@ static void nohz_balancer_kick(struct rq *rq)
kick_ilb(flags);
}
void nohz_balance_exit_idle(unsigned int 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.
*/
if (likely(cpumask_test_cpu(cpu, nohz.idle_cpus_mask))) {
cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
atomic_dec(&nohz.nr_cpus);
}
atomic_andnot(NOHZ_TICK_STOPPED, nohz_flags(cpu));
}
}
void set_cpu_sd_state_idle(void)
static void set_cpu_sd_state_busy(int cpu)
{
struct sched_domain *sd;
rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_llc, cpu));
if (!sd || !sd->nohz_idle)
goto unlock;
sd->nohz_idle = 0;
atomic_inc(&sd->shared->nr_busy_cpus);
unlock:
rcu_read_unlock();
}
void nohz_balance_exit_idle(struct rq *rq)
{
SCHED_WARN_ON(rq != this_rq());
if (likely(!rq->nohz_tick_stopped))
return;
rq->nohz_tick_stopped = 0;
cpumask_clear_cpu(rq->cpu, nohz.idle_cpus_mask);
atomic_dec(&nohz.nr_cpus);
set_cpu_sd_state_busy(rq->cpu);
}
static void set_cpu_sd_state_idle(int cpu)
{
struct sched_domain *sd;
int cpu = smp_processor_id();
rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_llc, cpu));
@ -9280,6 +9274,10 @@ void set_cpu_sd_state_idle(void)
*/
void nohz_balance_enter_idle(int cpu)
{
struct rq *rq = cpu_rq(cpu);
SCHED_WARN_ON(cpu != smp_processor_id());
/* If this CPU is going down, then nothing needs to be done: */
if (!cpu_active(cpu))
return;
@ -9288,16 +9286,19 @@ void nohz_balance_enter_idle(int cpu)
if (!housekeeping_cpu(cpu, HK_FLAG_SCHED))
return;
if (atomic_read(nohz_flags(cpu)) & NOHZ_TICK_STOPPED)
if (rq->nohz_tick_stopped)
return;
/* If we're a completely isolated CPU, we don't play: */
if (on_null_domain(cpu_rq(cpu)))
if (on_null_domain(rq))
return;
rq->nohz_tick_stopped = 1;
cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
atomic_inc(&nohz.nr_cpus);
atomic_or(NOHZ_TICK_STOPPED, nohz_flags(cpu));
set_cpu_sd_state_idle(cpu);
}
#else
static inline void nohz_balancer_kick(struct rq *rq) { }

11
kernel/sched/sched.h
View file

@ -764,6 +764,7 @@ struct rq {
unsigned long last_load_update_tick;
unsigned long last_blocked_load_update_tick;
#endif /* CONFIG_SMP */
unsigned int nohz_tick_stopped;
atomic_t nohz_flags;
#endif /* CONFIG_NO_HZ_COMMON */
@ -2035,11 +2036,9 @@ extern void cfs_bandwidth_usage_inc(void);
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_BALANCE_KICK_BIT 0
#define NOHZ_STATS_KICK_BIT 1
#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)
@ -2047,9 +2046,9 @@ extern void cfs_bandwidth_usage_dec(void);
#define nohz_flags(cpu) (&cpu_rq(cpu)->nohz_flags)
extern void nohz_balance_exit_idle(unsigned int cpu);
extern void nohz_balance_exit_idle(struct rq *rq);
#else
static inline void nohz_balance_exit_idle(unsigned int cpu) { }
static inline void nohz_balance_exit_idle(struct rq *rq) { }
#endif

7
kernel/time/tick-sched.c
View file

@ -954,13 +954,6 @@ void tick_nohz_idle_enter(void)
struct tick_sched *ts;
lockdep_assert_irqs_enabled();
/*
* Update the idle state in the scheduler domain hierarchy
* when tick_nohz_stop_sched_tick() is called from the idle loop.
* State will be updated to busy during the first busy tick after
* exiting idle.
*/
set_cpu_sd_state_idle();
local_irq_disable();