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

Rafael J. Wysocki
2018-04-06T08:10:57Z

On Friday, April 6, 2018 4:44:14 AM CEST Frederic Weisbecker wrote:
> 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;

This particular change breaks build, because tick_stopped is
accessed via __this_cpu_read() in tick_nohz_tick_stopped().

> + 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;
> };
>
>

So what about this? And moving the duplicated piece of got_idle_tick
manipulation on top of it?

---
From: Frederic Weisbecker <frederic@kernel.org>
Subject: [PATCH] nohz: Gather tick_sched booleans under a common flag field

Optimize the space and leave plenty of room for further flags.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
[ rjw: Do not use __this_cpu_read() to access tick_stopped and add
got_idle_tick to avoid overloading inidle ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
kernel/time/tick-sched.c | 12 +++++++-----
kernel/time/tick-sched.h | 12 ++++++++----
2 files changed, 15 insertions(+), 9 deletions(-)

Index: linux-pm/kernel/time/tick-sched.h
===================================================================
--- linux-pm.orig/kernel/time/tick-sched.h
+++ linux-pm/kernel/time/tick-sched.h
@@ -41,19 +41,24 @@ enum tick_nohz_mode {
* @timer_expires: Anticipated timer expiration time (in case sched tick is stopped)
* @timer_expires_base: Base time clock monotonic for @timer_expires
* @do_timer_lst: CPU was the last one doing do_timer before going idle
+ * @got_idle_tick: Tick timer function has run with @inidle set
*/
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;
+ unsigned int got_idle_tick : 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;
@@ -64,7 +69,6 @@ struct tick_sched {
u64 timer_expires_base;
u64 next_timer;
ktime_t idle_expires;
- int do_timer_last;
atomic_t tick_dep_mask;
};

Index: linux-pm/kernel/time/tick-sched.c
===================================================================
--- linux-pm.orig/kernel/time/tick-sched.c
+++ linux-pm/kernel/time/tick-sched.c
@@ -465,7 +465,9 @@ __setup("nohz=", setup_tick_nohz);

bool tick_nohz_tick_stopped(void)
{
- return __this_cpu_read(tick_cpu_sched.tick_stopped);
+ struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
+
+ return ts->tick_stopped;
}

bool tick_nohz_tick_stopped_cpu(int cpu)
@@ -1014,8 +1016,8 @@ bool tick_nohz_idle_got_tick(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

- if (ts->inidle > 1) {
- ts->inidle = 1;
+ if (ts->got_idle_tick) {
+ ts->got_idle_tick = 0;
return true;
}
return false;
@@ -1161,7 +1163,7 @@ static void tick_nohz_handler(struct clo
ktime_t now = ktime_get();

if (ts->inidle)
- ts->inidle = 2;
+ ts->got_idle_tick = 1;

dev->next_event = KTIME_MAX;

@@ -1261,7 +1263,7 @@ static enum hrtimer_restart tick_sched_t
ktime_t now = ktime_get();

if (ts->inidle)
- ts->inidle = 2;
+ ts->got_idle_tick = 1;

tick_sched_do_timer(now);