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From: Greg KH on 11 Aug 2010 20:40
2.6.32-stable review patch. If anyone has any objections, please let us know.

------------------

From: Martin Schwidefsky <schwidefsky(a)de.ibm.com>

commit eed3b9cf3fe3fcc7a50238dfcab63a63914e8f42 upstream.

On a system with NOHZ=y tick_check_idle calls tick_nohz_stop_idle and
tick_nohz_update_jiffies. Given the right conditions (ts->idle_active
and/or ts->tick_stopped) both function get a time stamp with ktime_get.
The same time stamp can be reused if both function require one.

On s390 this change has the additional benefit that gcc inlines the
tick_nohz_stop_idle function into tick_check_idle. The number of
instructions to execute tick_check_idle drops from 225 to 144
(without the ktime_get optimization it is 367 vs 215 instructions).

before:

0) | tick_check_idle() {
0) | tick_nohz_stop_idle() {
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.601 us | }
0) 1.765 us | }
0) 3.047 us | }
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.570 us | }
0) 1.727 us | }
0) | tick_do_update_jiffies64() {
0) 0.609 us | }
0) 8.055 us | }

after:

0) | tick_check_idle() {
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.617 us | }
0) 1.773 us | }
0) | tick_do_update_jiffies64() {
0) 0.593 us | }
0) 4.477 us | }

Signed-off-by: Martin Schwidefsky <schwidefsky(a)de.ibm.com>
Cc: john stultz <johnstul(a)us.ibm.com>
LKML-Reference: <20090929122533.206589318(a)de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de>
Acked-by: John Jolly <jjolly(a)suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
kernel/time/tick-sched.c | 62 +++++++++++++++++++++++++----------------------
1 file changed, 33 insertions(+), 29 deletions(-)

--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -134,18 +134,13 @@ __setup("nohz=", setup_tick_nohz);
* value. We do this unconditionally on any cpu, as we don't know whether the
* cpu, which has the update task assigned is in a long sleep.
*/
-static void tick_nohz_update_jiffies(void)
+static void tick_nohz_update_jiffies(ktime_t now)
{
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
unsigned long flags;
- ktime_t now;
-
- if (!ts->tick_stopped)
- return;

cpumask_clear_cpu(cpu, nohz_cpu_mask);
- now = ktime_get();
ts->idle_waketime = now;

local_irq_save(flags);
@@ -155,20 +150,17 @@ static void tick_nohz_update_jiffies(voi
touch_softlockup_watchdog();
}

-static void tick_nohz_stop_idle(int cpu)
+static void tick_nohz_stop_idle(int cpu, ktime_t now)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ktime_t delta;

- if (ts->idle_active) {
- ktime_t now, delta;
- now = ktime_get();
- delta = ktime_sub(now, ts->idle_entrytime);
- ts->idle_lastupdate = now;
- ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
- ts->idle_active = 0;
+ delta = ktime_sub(now, ts->idle_entrytime);
+ ts->idle_lastupdate = now;
+ ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
+ ts->idle_active = 0;

- sched_clock_idle_wakeup_event(0);
- }
+ sched_clock_idle_wakeup_event(0);
}

static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
@@ -463,7 +455,11 @@ void tick_nohz_restart_sched_tick(void)
ktime_t now;

local_irq_disable();
- tick_nohz_stop_idle(cpu);
+ if (ts->idle_active || (ts->inidle && ts->tick_stopped))
+ now = ktime_get();
+
+ if (ts->idle_active)
+ tick_nohz_stop_idle(cpu, now);

if (!ts->inidle || !ts->tick_stopped) {
ts->inidle = 0;
@@ -477,7 +473,6 @@ void tick_nohz_restart_sched_tick(void)

/* Update jiffies first */
select_nohz_load_balancer(0);
- now = ktime_get();
tick_do_update_jiffies64(now);
cpumask_clear_cpu(cpu, nohz_cpu_mask);

@@ -611,22 +606,18 @@ static void tick_nohz_switch_to_nohz(voi
* timer and do not touch the other magic bits which need to be done
* when idle is left.
*/
-static void tick_nohz_kick_tick(int cpu)
+static void tick_nohz_kick_tick(int cpu, ktime_t now)
{
#if 0
/* Switch back to 2.6.27 behaviour */

struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
- ktime_t delta, now;
-
- if (!ts->tick_stopped)
- return;
+ ktime_t delta;

/*
* Do not touch the tick device, when the next expiry is either
* already reached or less/equal than the tick period.
*/
- now = ktime_get();
delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
if (delta.tv64 <= tick_period.tv64)
return;
@@ -635,9 +626,26 @@ static void tick_nohz_kick_tick(int cpu)
#endif
}

+static inline void tick_check_nohz(int cpu)
+{
+ struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ktime_t now;
+
+ if (!ts->idle_active && !ts->tick_stopped)
+ return;
+ now = ktime_get();
+ if (ts->idle_active)
+ tick_nohz_stop_idle(cpu, now);
+ if (ts->tick_stopped) {
+ tick_nohz_update_jiffies(now);
+ tick_nohz_kick_tick(cpu, now);
+ }
+}
+
#else

static inline void tick_nohz_switch_to_nohz(void) { }
+static inline void tick_check_nohz(int cpu) { }

#endif /* NO_HZ */

@@ -647,11 +655,7 @@ static inline void tick_nohz_switch_to_n
void tick_check_idle(int cpu)
{
tick_check_oneshot_broadcast(cpu);
-#ifdef CONFIG_NO_HZ
- tick_nohz_stop_idle(cpu);
- tick_nohz_update_jiffies();
- tick_nohz_kick_tick(cpu);
-#endif
+ tick_check_nohz(cpu);
}

/*


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Prev: [077/111] Btrfs: Fix oopsen when dropping empty tree.
Next: [065/111] Btrfs: fix regression in orphan cleanup