linux-kernel - [PATCH 2/2] tick/nohz: Remove duplicate between tick_nohz_lowres_handler() and tick_nohz_highres

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Message-ID: <TYCP286MB2146338A68C0382DD17BDB6DC6BDA@TYCP286MB2146.JPNP286.PROD.OUTLOOK.COM>
Date:   Mon, 27 Nov 2023 16:31:18 +0800
From:   Peng Liu <pngliu@...mail.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     frederic@...nel.org, tglx@...utronix.de, mingo@...nel.org,
        linux-kernel@...r.kernel.org, liupeng17@...ovo.com
Subject: [PATCH 2/2] tick/nohz: Remove duplicate between tick_nohz_lowres_handler() and tick_nohz_highres_handler()

From: Peng Liu <liupeng17@...ovo.com>

tick_nohz_lowres_handler() does the same work as tick_nohz_highres_handler()
plus the clockevent device reprogramming, so should reuse the latter.

Signed-off-by: Peng Liu <liupeng17@...ovo.com>
---
 kernel/time/tick-sched.c | 31 +++++++++++--------------------
 1 file changed, 11 insertions(+), 20 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index cdebb6240efe..63422d6f3aa3 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1383,36 +1383,25 @@ void tick_nohz_idle_exit(void)
 	local_irq_enable();
 }
 
+static enum hrtimer_restart tick_nohz_highres_handler(struct hrtimer *timer);
+
 /*
  * In low-resolution mode, the tick handler must be implemented directly
  * at the clockevent level. hrtimer can't be used instead, because its
  * infrastructure actually relies on the tick itself as a backend in
  * low-resolution mode (see hrtimer_run_queues()).
  *
- * This low-resolution handler still makes use of some hrtimer APIs meanwhile
- * for convenience with expiration calculation and forwarding.
+ * This low-resolution handler still reuse tick_nohz_highres_handler() since
+ * most of the work is independent of the clockevent level.
  */
 static void tick_nohz_lowres_handler(struct clock_event_device *dev)
 {
 	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
-	struct pt_regs *regs = get_irq_regs();
-	ktime_t now = ktime_get();
 
 	dev->next_event = KTIME_MAX;
 
-	tick_sched_do_timer(ts, now);
-	tick_sched_handle(ts, regs);
-
-	/*
-	 * In dynticks mode, tick reprogram is deferred:
-	 * - to the idle task if in dynticks-idle
-	 * - to IRQ exit if in full-dynticks.
-	 */
-	if (likely(!ts->tick_stopped)) {
-		hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
+	if (likely(tick_nohz_highres_handler(&ts->sched_timer) == HRTIMER_RESTART))
 		tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
-	}
-
 }
 
 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
@@ -1481,10 +1470,7 @@ void tick_irq_enter(void)
 	tick_nohz_irq_enter();
 }
 
-/*
- * High resolution timer specific code
- */
-#ifdef CONFIG_HIGH_RES_TIMERS
+#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 /*
  * We rearm the timer until we get disabled by the idle code.
  * Called with interrupts disabled.
@@ -1519,7 +1505,12 @@ static enum hrtimer_restart tick_nohz_highres_handler(struct hrtimer *timer)
 
 	return HRTIMER_RESTART;
 }
+#endif
 
+/*
+ * High resolution timer specific code
+ */
+#ifdef CONFIG_HIGH_RES_TIMERS
 static int sched_skew_tick;
 
 static int __init skew_tick(char *str)
-- 
2.34.1