[PATCH v3 1/2] tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()

[Peng Liu]

From: Peng Liu <liupeng17@xxxxxxxxxx>

The ts->sched_timer initialization work of tick_nohz_switch_to_nohz()
is almost the same as that of tick_setup_sched_timer(), so adjust the
latter to get it reused by tick_nohz_switch_to_nohz().

This also makes low-res mode sched_timer benefit from the tick skew
boot option.

Signed-off-by: Peng Liu <liupeng17@xxxxxxxxxx>
---
Changes in v3:
- Remove the first``#ifdef CONFIG_HIGH_RES_TIMERS'' in tick_setup_sched_timer()
  in patch 2/2
- Add comment on sched_skew_tick introduced to low-res mode tick_sched setup
- Replace hrtimer_forward() with hrtimer_forward_now() in tick_setup_sched_timer()
- Remove the sedond ``#ifdef CONFIG_HIGH_RES_TIMERS'' in tick_setup_sched_timer()
- Move tick_nohz_highres_handler() ahead to avoid additional declaration
Changes in v2:
- Fix build warning: Function parameter or member 'mode' not described in
  'tick_setup_sched_timer'
- Fix build error: use of undeclared identifier 'tick_nohz_highres_handler'
- Fix build error: use of undeclared identifier 'sched_skew_tick'
---
 kernel/time/hrtimer.c    |  2 +-
 kernel/time/tick-sched.c | 38 +++++++++++++++++---------------------
 kernel/time/tick-sched.h |  2 +-
 3 files changed, 19 insertions(+), 23 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 760793998cdd..355b5a957f7f 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -746,7 +746,7 @@ static void hrtimer_switch_to_hres(void)
 	base->hres_active = 1;
 	hrtimer_resolution = HIGH_RES_NSEC;
 
-	tick_setup_sched_timer();
+	tick_setup_sched_timer(NOHZ_MODE_HIGHRES);
 	/* "Retrigger" the interrupt to get things going */
 	retrigger_next_event(NULL);
 }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index be77b021e5d6..d25039f07838 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1430,9 +1430,6 @@ static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
  */
 static void tick_nohz_switch_to_nohz(void)
 {
-	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
-	ktime_t next;
-
 	if (!tick_nohz_enabled)
 		return;
 
@@ -1441,16 +1438,9 @@ static void tick_nohz_switch_to_nohz(void)
 
 	/*
 	 * Recycle the hrtimer in 'ts', so we can share the
-	 * hrtimer_forward_now() function with the highres code.
+	 * highres code.
 	 */
-	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
-	/* Get the next period */
-	next = tick_init_jiffy_update();
-
-	hrtimer_set_expires(&ts->sched_timer, next);
-	hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
-	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
-	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
+	tick_setup_sched_timer(NOHZ_MODE_LOWRES);
 }
 
 static inline void tick_nohz_irq_enter(void)
@@ -1529,7 +1519,9 @@ static enum hrtimer_restart tick_nohz_highres_handler(struct hrtimer *timer)
 
 	return HRTIMER_RESTART;
 }
+#endif /* HIGH_RES_TIMERS */
 
+#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 static int sched_skew_tick;
 
 static int __init skew_tick(char *str)
@@ -1542,15 +1534,18 @@ early_param("skew_tick", skew_tick);
 
 /**
  * tick_setup_sched_timer - setup the tick emulation timer
+ * @mode: tick_nohz_mode to setup for
  */
-void tick_setup_sched_timer(void)
+void tick_setup_sched_timer(int mode)
 {
 	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
-	ktime_t now = ktime_get();
 
 	/* Emulate tick processing via per-CPU hrtimers: */
 	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
-	ts->sched_timer.function = tick_nohz_highres_handler;
+#ifdef CONFIG_HIGH_RES_TIMERS
+	if (mode == NOHZ_MODE_HIGHRES)
+		ts->sched_timer.function = tick_nohz_highres_handler;
+#endif
 
 	/* Get the next period (per-CPU) */
 	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
@@ -1563,13 +1558,14 @@ void tick_setup_sched_timer(void)
 		hrtimer_add_expires_ns(&ts->sched_timer, offset);
 	}
 
-	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
-	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
-	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
+	hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
+	if (mode == NOHZ_MODE_HIGHRES)
+		hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
+	else
+		tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
+	tick_nohz_activate(ts, mode);
 }
-#endif /* HIGH_RES_TIMERS */
 
-#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 void tick_cancel_sched_timer(int cpu)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
@@ -1581,7 +1577,7 @@ void tick_cancel_sched_timer(int cpu)
 
 	memset(ts, 0, sizeof(*ts));
 }
-#endif
+#endif /* CONFIG_NO_HZ_COMMON || CONFIG_HIGH_RES_TIMERS */
 
 /*
  * Async notification about clocksource changes
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index 5ed5a9d41d5a..35808bbb8a47 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -102,7 +102,7 @@ struct tick_sched {
 
 extern struct tick_sched *tick_get_tick_sched(int cpu);
 
-extern void tick_setup_sched_timer(void);
+extern void tick_setup_sched_timer(int mode);
 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 extern void tick_cancel_sched_timer(int cpu);
 #else
-- 
2.34.1