Re: [PATCH v9 05/10] cpuidle: Return nohz hint from cpuidle_select()

Frederic Weisbecker
2018-04-06T02:44:20Z

On Wed, Apr 04, 2018 at 10:39:50AM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Index: linux-pm/kernel/time/tick-sched.c
> ===================================================================
> --- linux-pm.orig/kernel/time/tick-sched.c
> +++ linux-pm/kernel/time/tick-sched.c
> @@ -991,6 +991,20 @@ void tick_nohz_irq_exit(void)
> }
>
> /**
> + * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
> + */
> +bool tick_nohz_idle_got_tick(void)
> +{
> + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
> +
> + if (ts->inidle > 1) {
> + ts->inidle = 1;
> + return true;
> + }
> + return false;
> +}
> +
> +/**
> * tick_nohz_get_sleep_length - return the length of the current sleep
> *
> * Called from power state control code with interrupts disabled
> @@ -1101,6 +1115,9 @@ static void tick_nohz_handler(struct clo
> struct pt_regs *regs = get_irq_regs();
> ktime_t now = ktime_get();
>
> + if (ts->inidle)
> + ts->inidle = 2;
> +

You can move that to tick_sched_do_timer() to avoid code duplication.

Also these constants are very opaque. And even with proper symbols it wouldn't look
right to extend ts->inidle that way.

Perhaps you should add a field such as ts->got_idle_tick under the boolean fields
after the below patch:

--
>From c7b2ca5a4c512517ddfeb9f922d5999f82542ced Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic@kernel.org>
Date: Fri, 6 Apr 2018 04:32:37 +0200
Subject: [PATCH] nohz: Gather tick_sched booleans under a common flag field

This optimize the space and leave plenty of room for further flags.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
kernel/time/tick-sched.h | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index 954b43d..38f24dc 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -45,14 +45,17 @@ struct tick_sched {
struct hrtimer sched_timer;
unsigned long check_clocks;
enum tick_nohz_mode nohz_mode;
+
+ unsigned int inidle : 1;
+ unsigned int tick_stopped : 1;
+ unsigned int idle_active : 1;
+ unsigned int do_timer_last : 1;
+
ktime_t last_tick;
ktime_t next_tick;
- int inidle;
- int tick_stopped;
unsigned long idle_jiffies;
unsigned long idle_calls;
unsigned long idle_sleeps;
- int idle_active;
ktime_t idle_entrytime;
ktime_t idle_waketime;
ktime_t idle_exittime;
@@ -62,7 +65,6 @@ struct tick_sched {
unsigned long last_jiffies;
u64 next_timer;
ktime_t idle_expires;
- int do_timer_last;
atomic_t tick_dep_mask;
};

--
2.7.4