[PATCH 02/10] tick/nohz: Add tick_nohz_full_this_cpu()

[Frederic Weisbecker]

Optimize further the check for local full dynticks CPU. Testing directly
tick_nohz_full_cpu(smp_processor_id()) is suboptimal because the
compiler first fetches the CPU number and only then processes the
static key.

It's best to evaluate the static branch before anything. Provide with a
function that handles that correctly and convert some users along.

Signed-off-by: Frederic Weisbecker <frede...@kernel.org>
Cc: Yunfeng Ye <yeyunf...@huawei.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Marcelo Tosatti <mtosa...@redhat.com>
Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
---
 include/linux/tick.h     | 11 ++++++++++-
 kernel/time/tick-sched.c | 12 +++++-------
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 7340613c7eff..bfc96cbe955c 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -193,6 +193,14 @@ static inline bool tick_nohz_full_cpu(int cpu)
        return cpumask_test_cpu(cpu, tick_nohz_full_mask);
 }
 
+static inline bool tick_nohz_full_this_cpu(void)
+{
+       if (!tick_nohz_full_enabled())
+               return false;
+
+       return cpumask_test_cpu(smp_processor_id(), tick_nohz_full_mask);
+}
+
 static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask)
 {
        if (tick_nohz_full_enabled())
@@ -271,6 +279,7 @@ extern void __init tick_nohz_full_setup(cpumask_var_t 
cpumask);
 #else
 static inline bool tick_nohz_full_enabled(void) { return false; }
 static inline bool tick_nohz_full_cpu(int cpu) { return false; }
+static inline bool tick_nohz_full_this_cpu(void) { return false; }
 static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
 
 static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
@@ -296,7 +305,7 @@ static inline void tick_nohz_full_setup(cpumask_var_t 
cpumask) { }
 
 static inline void tick_nohz_task_switch(void)
 {
-       if (tick_nohz_full_enabled())
+       if (tick_nohz_full_this_cpu())
                __tick_nohz_task_switch();
 }
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 22b6a46818cf..af76cfa51b57 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -304,7 +304,7 @@ static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) 
=
  */
 static void tick_nohz_full_kick(void)
 {
-       if (!tick_nohz_full_cpu(smp_processor_id()))
+       if (!tick_nohz_full_this_cpu())
                return;
 
        irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
@@ -452,9 +452,6 @@ void __tick_nohz_task_switch(void)
 
        local_irq_save(flags);
 
-       if (!tick_nohz_full_cpu(smp_processor_id()))
-               goto out;
-
        ts = this_cpu_ptr(&tick_cpu_sched);
 
        if (ts->tick_stopped) {
@@ -462,7 +459,6 @@ void __tick_nohz_task_switch(void)
                    atomic_read(&current->signal->tick_dep_mask))
                        tick_nohz_full_kick();
        }
-out:
        local_irq_restore(flags);
 }
 
@@ -929,14 +925,16 @@ static void tick_nohz_restart_sched_tick(struct 
tick_sched *ts, ktime_t now)
 static void tick_nohz_full_update_tick(struct tick_sched *ts)
 {
 #ifdef CONFIG_NO_HZ_FULL
-       int cpu = smp_processor_id();
+       int cpu;
 
-       if (!tick_nohz_full_cpu(cpu))
+       if (!tick_nohz_full_this_cpu())
                return;
 
        if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
                return;
 
+       cpu = smp_processor_id();
+
        if (can_stop_full_tick(cpu, ts))
                tick_nohz_stop_sched_tick(ts, cpu);
        else if (ts->tick_stopped)
-- 
2.25.1