linux-kernel - Re: [PATCH] tick: shift tick_nohz_switch_to_nohz() from tick_check_oneshot_change() to hrtimer_run

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Date: Sat, 1 Jun 2024 16:56:52 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tick: shift tick_nohz_switch_to_nohz() from
 tick_check_oneshot_change() to hrtimer_run_queues()

On 05/30, Frederic Weisbecker wrote:
>
> tick_nohz_switch_to_nohz() is only built with CONFIG_NO_HZ_COMMON
>
> You will have a build issue with CONFIG_HIGH_RES_TIMER && !CONFIG_NO_HZ_COMMON

Thanks again.

At first glance this patch needs a simple fixup below. I'll recheck and
send V2.

NO_HZ_COMMON selects TICK_ONESHOT. But even if it didn't,
tick_check_oneshot_change() is dummy inline "return 0" without
CONFIG_TICK_ONESHOT, hrtimer_run_queues() will never try to
call tick_nohz_switch_to_nohz().

Oleg.


--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -112,7 +112,6 @@ static inline bool tick_oneshot_possible(void) { return true; }
 extern int tick_oneshot_mode_active(void);
 extern void tick_clock_notify(void);
 extern int tick_check_oneshot_change(void);
-extern void tick_nohz_switch_to_nohz(void);
 extern int tick_init_highres(void);
 #else /* !CONFIG_TICK_ONESHOT: */
 static inline
@@ -126,7 +125,6 @@ static inline bool tick_oneshot_possible(void) { return false; }
 static inline int tick_oneshot_mode_active(void) { return 0; }
 static inline void tick_clock_notify(void) { }
 static inline int tick_check_oneshot_change(void) { return 0; }
-static inline void tick_nohz_switch_to_nohz(void) { }
 #endif /* !CONFIG_TICK_ONESHOT */
 
 /* Functions related to oneshot broadcasting */
@@ -159,6 +157,7 @@ static inline void tick_nohz_init(void) { }
 #endif
 
 #ifdef CONFIG_NO_HZ_COMMON
+extern void tick_nohz_switch_to_nohz(void);
 extern unsigned long tick_nohz_active;
 extern void timers_update_nohz(void);
 extern u64 get_jiffies_update(unsigned long *basej);
@@ -173,6 +172,7 @@ extern bool timer_base_is_idle(void);
 extern void timer_expire_remote(unsigned int cpu);
 # endif
 #else /* CONFIG_NO_HZ_COMMON */
+static inline void tick_nohz_switch_to_nohz(void) { }
 static inline void timers_update_nohz(void) { }
 #define tick_nohz_active (0)
 #endif