linux-kernel - [RFC][PATCH 3/3] Kconfig: Add CONFIG_DYN_HZ_DEFAULT to specify the default dynhz= boot option value

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Message-ID: <20250128063301.3879317-4-jstultz@google.com>
Date: Mon, 27 Jan 2025 22:32:55 -0800
From: John Stultz <jstultz@...gle.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: John Stultz <jstultz@...gle.com>, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Frederic Weisbecker <frederic@...nel.org>, Ingo Molnar <mingo@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, Stephen Boyd <sboyd@...nel.org>, 
	Yury Norov <yury.norov@...il.com>, Bitao Hu <yaoma@...ux.alibaba.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, kernel-team@...roid.com
Subject: [RFC][PATCH 3/3] Kconfig: Add CONFIG_DYN_HZ_DEFAULT to specify the
 default dynhz= boot option value

Allow a default dynhz= boot option value to be specified via config.

Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Stephen Boyd <sboyd@...nel.org>
Cc: Yury Norov <yury.norov@...il.com>
Cc: Bitao Hu <yaoma@...ux.alibaba.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel-team@...roid.com
Signed-off-by: John Stultz <jstultz@...gle.com>
---
 kernel/Kconfig.hz         | 10 ++++++++++
 kernel/time/tick-common.c |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/Kconfig.hz b/kernel/Kconfig.hz
index 76714317674c5..27ad1400ad64e 100644
--- a/kernel/Kconfig.hz
+++ b/kernel/Kconfig.hz
@@ -64,5 +64,15 @@ config DYN_HZ
 	 build time configured HZ value.
 	 If you are unsure, say no.
 
+config DYN_HZ_DEFAULT
+	int "Default DynHZ value (valid range: 100-CONFIG_HZ)"
+	depends on DYN_HZ
+	default HZ
+        range 100 HZ
+	help
+	 Default value for dynhz. This allows ticks to be configured
+	 to arrive at slower than HZ rates. This is useful when you
+	 want to allow boot-time configurable tick rates.
+
 config SCHED_HRTICK
 	def_bool HIGH_RES_TIMERS
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 75fd9dadb8273..46463bfb75d3d 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -81,7 +81,7 @@ int tick_is_oneshot_available(void)
 }
 
 #ifdef CONFIG_DYN_HZ
-long long dyn_tick_nsec = TICK_NSEC;
+long long dyn_tick_nsec = TICK_NSEC * HZ / CONFIG_DYN_HZ_DEFAULT;
 
 static int __init set_dyn_hz(char *str)
 {
-- 
2.48.1.262.g85cc9f2d1e-goog