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Message-ID: <2697163.FknhNRV3Rg@aspire.rjw.lan>
Date: Fri, 09 Mar 2018 10:36:56 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Peter Zijlstra <peterz@...radead.org>,
Linux PM <linux-pm@...r.kernel.org>,
Frederic Weisbecker <fweisbec@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Paul McKenney <paulmck@...ux.vnet.ibm.com>,
Thomas Ilsche <thomas.ilsche@...dresden.de>,
Doug Smythies <dsmythies@...us.net>,
Rik van Riel <riel@...riel.com>,
Aubrey Li <aubrey.li@...ux.intel.com>,
Mike Galbraith <mgalbraith@...e.de>,
LKML <linux-kernel@...r.kernel.org>
Subject: [RFC/RFT][PATCH v3 1/6] time: tick-sched: Reorganize idle tick management code
From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Prepare the scheduler tick code for reworking the idle loop to
avoid stopping the tick in some cases.
Move away the tick_nohz_start_idle() invocation from
__tick_nohz_idle_enter(), rename the latter to
__tick_nohz_idle_stop_tick() and define tick_nohz_idle_stop_tick()
as a wrapper around it for calling it from the outside.
Make tick_nohz_idle_enter() only call tick_nohz_start_idle() instead
of calling the entire __tick_nohz_idle_enter(), add another wrapper
disabling and enabling interrupts around tick_nohz_idle_stop_tick()
and make the current callers of tick_nohz_idle_enter() call it too
to retain their current functionality.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
arch/x86/xen/smp_pv.c | 1 +
include/linux/tick.h | 9 +++++++++
kernel/sched/idle.c | 1 +
kernel/time/tick-sched.c | 46 +++++++++++++++++++++++++---------------------
4 files changed, 36 insertions(+), 21 deletions(-)
Index: linux-pm/include/linux/tick.h
===================================================================
--- linux-pm.orig/include/linux/tick.h
+++ linux-pm/include/linux/tick.h
@@ -114,6 +114,7 @@ enum tick_dep_bits {
#ifdef CONFIG_NO_HZ_COMMON
extern bool tick_nohz_enabled;
extern int tick_nohz_tick_stopped(void);
+extern void tick_nohz_idle_stop_tick(void);
extern void tick_nohz_idle_enter(void);
extern void tick_nohz_idle_exit(void);
extern void tick_nohz_irq_exit(void);
@@ -125,6 +126,7 @@ extern u64 get_cpu_iowait_time_us(int cp
#else /* !CONFIG_NO_HZ_COMMON */
#define tick_nohz_enabled (0)
static inline int tick_nohz_tick_stopped(void) { return 0; }
+static inline void tick_nohz_idle_stop_tick(void) { }
static inline void tick_nohz_idle_enter(void) { }
static inline void tick_nohz_idle_exit(void) { }
@@ -136,6 +138,13 @@ static inline u64 get_cpu_idle_time_us(i
static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
#endif /* !CONFIG_NO_HZ_COMMON */
+static inline void tick_nohz_idle_stop_tick_protected(void)
+{
+ local_irq_disable();
+ tick_nohz_idle_stop_tick();
+ local_irq_enable();
+}
+
#ifdef CONFIG_NO_HZ_FULL
extern bool tick_nohz_full_running;
extern cpumask_var_t tick_nohz_full_mask;
Index: linux-pm/kernel/time/tick-sched.c
===================================================================
--- linux-pm.orig/kernel/time/tick-sched.c
+++ linux-pm/kernel/time/tick-sched.c
@@ -539,14 +539,11 @@ static void tick_nohz_stop_idle(struct t
sched_clock_idle_wakeup_event();
}
-static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
+static void tick_nohz_start_idle(struct tick_sched *ts)
{
- ktime_t now = ktime_get();
-
- ts->idle_entrytime = now;
+ ts->idle_entrytime = ktime_get();
ts->idle_active = 1;
sched_clock_idle_sleep_event();
- return now;
}
/**
@@ -911,19 +908,21 @@ static bool can_stop_idle_tick(int cpu,
return true;
}
-static void __tick_nohz_idle_enter(struct tick_sched *ts)
+static void __tick_nohz_idle_stop_tick(struct tick_sched *ts)
{
- ktime_t now, expires;
+ ktime_t expires;
int cpu = smp_processor_id();
- now = tick_nohz_start_idle(ts);
-
if (can_stop_idle_tick(cpu, ts)) {
int was_stopped = ts->tick_stopped;
ts->idle_calls++;
- expires = tick_nohz_stop_sched_tick(ts, now, cpu);
+ /*
+ * The idle entry time should be a sufficient approximation of
+ * the current time at this point.
+ */
+ expires = tick_nohz_stop_sched_tick(ts, ts->idle_entrytime, cpu);
if (expires > 0LL) {
ts->idle_sleeps++;
ts->idle_expires = expires;
@@ -937,16 +936,19 @@ static void __tick_nohz_idle_enter(struc
}
/**
- * tick_nohz_idle_enter - stop the idle tick from the idle task
+ * tick_nohz_idle_stop_tick - stop the idle tick from the idle task
*
* When the next event is more than a tick into the future, stop the idle tick
- * Called when we start the idle loop.
- *
- * The arch is responsible of calling:
+ */
+void tick_nohz_idle_stop_tick(void)
+{
+ __tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched));
+}
+
+/**
+ * tick_nohz_idle_enter - prepare for entering idle on the current CPU
*
- * - rcu_idle_enter() after its last use of RCU before the CPU is put
- * to sleep.
- * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
+ * Called when we start the idle loop.
*/
void tick_nohz_idle_enter(void)
{
@@ -965,7 +967,7 @@ void tick_nohz_idle_enter(void)
ts = this_cpu_ptr(&tick_cpu_sched);
ts->inidle = 1;
- __tick_nohz_idle_enter(ts);
+ tick_nohz_start_idle(ts);
local_irq_enable();
}
@@ -982,10 +984,12 @@ void tick_nohz_irq_exit(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
- if (ts->inidle)
- __tick_nohz_idle_enter(ts);
- else
+ if (ts->inidle) {
+ tick_nohz_start_idle(ts);
+ __tick_nohz_idle_stop_tick(ts);
+ } else {
tick_nohz_full_update_tick(ts);
+ }
}
/**
Index: linux-pm/arch/x86/xen/smp_pv.c
===================================================================
--- linux-pm.orig/arch/x86/xen/smp_pv.c
+++ linux-pm/arch/x86/xen/smp_pv.c
@@ -425,6 +425,7 @@ static void xen_pv_play_dead(void) /* us
* data back is to call:
*/
tick_nohz_idle_enter();
+ tick_nohz_idle_stop_tick_protected();
cpuhp_online_idle(CPUHP_AP_ONLINE_IDLE);
}
Index: linux-pm/kernel/sched/idle.c
===================================================================
--- linux-pm.orig/kernel/sched/idle.c
+++ linux-pm/kernel/sched/idle.c
@@ -221,6 +221,7 @@ static void do_idle(void)
__current_set_polling();
tick_nohz_idle_enter();
+ tick_nohz_idle_stop_tick_protected();
while (!need_resched()) {
check_pgt_cache();
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