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nohz: Reuse ktime in sub-functions of tick_check_idle. 

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@de.ibm.com>
Cc: john stultz <johnstul@us.ibm.com>
LKML-Reference: <20090929122533.206589318@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Martin Schwidefsky 2009-09-29 14:25:15 +02:00 committed by Thomas Gleixner
parent 7bc7d63745
commit eed3b9cf3f
1 changed files with 33 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

62
kernel/time/tick-sched.c
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@ -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(void)
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)
@ -431,7 +423,11 @@ 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;
@ -445,7 +441,6 @@ 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);
@ -579,22 +574,18 @@ static void tick_nohz_switch_to_nohz(void)
* 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;
@ -603,9 +594,26 @@ 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 */
@ -615,11 +623,7 @@ static inline void tick_nohz_switch_to_nohz(void) { }
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);
}
/*