[PATCH] tick/nohz_full: turn tick_do_timer_boot_cpu into boot_cpu_is_nohz_full

Oleg Nesterov
2024-05-30T12:42:24Z

We don't need to record the cpu number of the nohz_full boot CPU, a simple
boolean is enough.

We could even kill it along with #ifdef, the "else if" branch could check
tick_nohz_full_cpu(tick_do_timer_cpu) && !tick_nohz_full_cpu(cpu).

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/time/tick-common.c | 24 ++++++++----------------
1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 27d0018c8b05..9829a2cda072 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -49,15 +49,6 @@ ktime_t tick_next_period;
* procedure also covers cpu hotplug.
*/
int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
-#ifdef CONFIG_NO_HZ_FULL
-/*
- * tick_do_timer_boot_cpu indicates the boot CPU temporarily owns
- * tick_do_timer_cpu and it should be taken over by an eligible secondary
- * when one comes online.
- */
-static int tick_do_timer_boot_cpu __read_mostly = -1;
-#endif
-
/*
* Debugging: see timer_list.c
*/
@@ -178,9 +169,13 @@ void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
}
}

+#ifdef CONFIG_NO_HZ_FULL
/*
- * Setup the tick device
+ * Iindicates that the boot CPU temporarily owns tick_do_timer_cpu.
*/
+static bool boot_cpu_is_nohz_full __read_mostly;
+#endif
+
static void tick_setup_device(struct tick_device *td,
struct clock_event_device *newdev, int cpu,
const struct cpumask *cpumask)
@@ -205,12 +200,9 @@ static void tick_setup_device(struct tick_device *td,
* first housekeeping secondary will take do_timer()
* from us.
*/
- if (tick_nohz_full_cpu(cpu))
- tick_do_timer_boot_cpu = cpu;
-
- } else if (tick_do_timer_boot_cpu != -1 &&
- !tick_nohz_full_cpu(cpu)) {
- tick_do_timer_boot_cpu = -1;
+ boot_cpu_is_nohz_full = tick_nohz_full_cpu(cpu);
+ } else if (boot_cpu_is_nohz_full && !tick_nohz_full_cpu(cpu)) {
+ boot_cpu_is_nohz_full = false;
/*
* The boot CPU will stay in periodic (NOHZ disabled)
* mode until clocksource_done_booting() called after
--
2.25.1.362.g51ebf55