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

Rafael J. Wysocki
2018-04-06T12:56:37Z

On Friday, April 6, 2018 10:11:04 AM CEST Rafael J. Wysocki wrote:
> 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)
> > > }

[cut]

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

And appended is a patch to get rid of the code duplication (on top of the one
below), for completeness.

> ---
> 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);
>

---
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH] nohz: Avoid duplication of code related to got_idle_tick

Move the code setting ts->got_idle_tick into tick_sched_do_timer() to
avoid code duplication.

No intentional changes in functionality.

Suggested-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
kernel/time/tick-sched.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)

Index: linux-pm/kernel/time/tick-sched.c
===================================================================
--- linux-pm.orig/kernel/time/tick-sched.c
+++ linux-pm/kernel/time/tick-sched.c
@@ -113,8 +113,7 @@ static ktime_t tick_init_jiffy_update(vo
return period;
}

-
-static void tick_sched_do_timer(ktime_t now)
+static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
{
int cpu = smp_processor_id();

@@ -134,6 +133,9 @@ static void tick_sched_do_timer(ktime_t
/* Check, if the jiffies need an update */
if (tick_do_timer_cpu == cpu)
tick_do_update_jiffies64(now);
+
+ if (ts->inidle)
+ ts->got_idle_tick = 1;
}

static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
@@ -1162,12 +1164,9 @@ static void tick_nohz_handler(struct clo
struct pt_regs *regs = get_irq_regs();
ktime_t now = ktime_get();

- if (ts->inidle)
- ts->got_idle_tick = 1;
-
dev->next_event = KTIME_MAX;

- tick_sched_do_timer(now);
+ tick_sched_do_timer(ts, now);
tick_sched_handle(ts, regs);

/* No need to reprogram if we are running tickless */
@@ -1262,10 +1261,7 @@ static enum hrtimer_restart tick_sched_t
struct pt_regs *regs = get_irq_regs();
ktime_t now = ktime_get();

- if (ts->inidle)
- ts->got_idle_tick = 1;
-
- tick_sched_do_timer(now);
+ tick_sched_do_timer(ts, now);

/*
* Do not call, when we are not in irq context and have