tick/nohz: Conditionally restart tick on idle exit

In nohz_full mode, switching from idle to a task will unconditionally
issue a tick restart. If the task is alone in the runqueue or is the
highest priority, the tick will fire once then eventually stop. But that
alone is still undesired noise.

Therefore, only restart the tick on idle exit when it's strictly
necessary.

Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210512232924.150322-3-frederic@kernel.org

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 828b091501ca4571040e88b336276ee39b7a0cb2..05c1ce1034d6c42ab8709277688c20323793684f 100644 (file)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -926,22 +926,28 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
        tick_nohz_restart(ts, now);
 }
 
-static void tick_nohz_full_update_tick(struct tick_sched *ts)
+static void __tick_nohz_full_update_tick(struct tick_sched *ts,
+                                        ktime_t now)
 {
 #ifdef CONFIG_NO_HZ_FULL
        int cpu = smp_processor_id();
 
-       if (!tick_nohz_full_cpu(cpu))
+       if (can_stop_full_tick(cpu, ts))
+               tick_nohz_stop_sched_tick(ts, cpu);
+       else if (ts->tick_stopped)
+               tick_nohz_restart_sched_tick(ts, now);
+#endif
+}
+
+static void tick_nohz_full_update_tick(struct tick_sched *ts)
+{
+       if (!tick_nohz_full_cpu(smp_processor_id()))
                return;
 
        if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
                return;
 
-       if (can_stop_full_tick(cpu, ts))
-               tick_nohz_stop_sched_tick(ts, cpu);
-       else if (ts->tick_stopped)
-               tick_nohz_restart_sched_tick(ts, ktime_get());
-#endif
+       __tick_nohz_full_update_tick(ts, ktime_get());
 }
 
 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
@@ -1209,18 +1215,24 @@ static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
 #endif
 }
 
-static void __tick_nohz_idle_restart_tick(struct tick_sched *ts, ktime_t now)
+void tick_nohz_idle_restart_tick(void)
 {
-       tick_nohz_restart_sched_tick(ts, now);
-       tick_nohz_account_idle_ticks(ts);
+       struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
+
+       if (ts->tick_stopped) {
+               tick_nohz_restart_sched_tick(ts, ktime_get());
+               tick_nohz_account_idle_ticks(ts);
+       }
 }
 
-void tick_nohz_idle_restart_tick(void)
+static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now)
 {
-       struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
+       if (tick_nohz_full_cpu(smp_processor_id()))
+               __tick_nohz_full_update_tick(ts, now);
+       else
+               tick_nohz_restart_sched_tick(ts, now);
 
-       if (ts->tick_stopped)
-               __tick_nohz_idle_restart_tick(ts, ktime_get());
+       tick_nohz_account_idle_ticks(ts);
 }
 
 /**
@@ -1252,7 +1264,7 @@ void tick_nohz_idle_exit(void)
                tick_nohz_stop_idle(ts, now);
 
        if (tick_stopped)
-               __tick_nohz_idle_restart_tick(ts, now);
+               tick_nohz_idle_update_tick(ts, now);
 
        local_irq_enable();
 }