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

[John Stultz <jstultz@google.com>]

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

Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Bitao Hu <yaoma@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: kernel-team@android.com
Signed-off-by: John Stultz <jstultz@google.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