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time: track accurate idle time with tick_sched.idle_sleeptime 

Current idle time in kstat is based on jiffies and is coarse grained.
tick_sched.idle_sleeptime is making some attempt to keep track of idle time
in a fine grained manner.  But, it is not handling the time spent in
interrupts fully.

Make tick_sched.idle_sleeptime accurate with respect to time spent on
handling interrupts and also add tick_sched.idle_lastupdate, which keeps
track of last time when idle_sleeptime was updated.

This statistics will be crucial for cpufreq-ondemand governor, which can
shed some conservative gaurd band that is uses today while setting the
frequency.  The ondemand changes that uses the exact idle time is coming
soon.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Venki Pallipadi 2008-01-30 13:30:04 +01:00 committed by Ingo Molnar
parent bbe4d18ac2
commit 6378ddb592
3 changed files with 62 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/tick.h
View File

@ -51,8 +51,10 @@ struct tick_sched {
unsigned long idle_jiffies;
unsigned long idle_calls;
unsigned long idle_sleeps;
int idle_active;
ktime_t idle_entrytime;
ktime_t idle_sleeptime;
ktime_t idle_lastupdate;
ktime_t sleep_length;
unsigned long last_jiffies;
unsigned long next_jiffies;
@ -103,6 +105,8 @@ extern void tick_nohz_stop_sched_tick(void);
extern void tick_nohz_restart_sched_tick(void);
extern void tick_nohz_update_jiffies(void);
extern ktime_t tick_nohz_get_sleep_length(void);
extern void tick_nohz_stop_idle(int cpu);
extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
# else
static inline void tick_nohz_stop_sched_tick(void) { }
static inline void tick_nohz_restart_sched_tick(void) { }
@ -113,6 +117,8 @@ static inline ktime_t tick_nohz_get_sleep_length(void)
return len;
}
static inline void tick_nohz_stop_idle(int cpu) { }
static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return 0; }
# endif /* !NO_HZ */
#endif

7
kernel/softirq.c
View File

@ -280,9 +280,14 @@ asmlinkage void do_softirq(void)
*/
void irq_enter(void)
{
#ifdef CONFIG_NO_HZ
int cpu = smp_processor_id();
if (idle_cpu(cpu) && !in_interrupt())
tick_nohz_stop_idle(cpu);
#endif
__irq_enter();
#ifdef CONFIG_NO_HZ
if (idle_cpu(smp_processor_id()))
if (idle_cpu(cpu))
tick_nohz_update_jiffies();
#endif
}

74
kernel/time/tick-sched.c
View File

@ -143,6 +143,44 @@ void tick_nohz_update_jiffies(void)
local_irq_restore(flags);
}
void tick_nohz_stop_idle(int cpu)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
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;
}
}
static ktime_t tick_nohz_start_idle(int cpu)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
ktime_t now, delta;
now = ktime_get();
if (ts->idle_active) {
delta = ktime_sub(now, ts->idle_entrytime);
ts->idle_lastupdate = now;
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
}
ts->idle_entrytime = now;
ts->idle_active = 1;
return now;
}
u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
*last_update_time = ktime_to_us(ts->idle_lastupdate);
return ktime_to_us(ts->idle_sleeptime);
}
/**
* tick_nohz_stop_sched_tick - stop the idle tick from the idle task
*
@ -155,13 +193,14 @@ void tick_nohz_stop_sched_tick(void)
unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
unsigned long rt_jiffies;
struct tick_sched *ts;
ktime_t last_update, expires, now, delta;
ktime_t last_update, expires, now;
struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
int cpu;
local_irq_save(flags);
cpu = smp_processor_id();
now = tick_nohz_start_idle(cpu);
ts = &per_cpu(tick_cpu_sched, cpu);
/*
@ -193,19 +232,7 @@ void tick_nohz_stop_sched_tick(void)
}
}
now = ktime_get();
/*
* When called from irq_exit we need to account the idle sleep time
* correctly.
*/
if (ts->tick_stopped) {
delta = ktime_sub(now, ts->idle_entrytime);
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
}
ts->idle_entrytime = now;
ts->idle_calls++;
/* Read jiffies and the time when jiffies were updated last */
do {
seq = read_seqbegin(&xtime_lock);
@ -337,23 +364,22 @@ void tick_nohz_restart_sched_tick(void)
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
unsigned long ticks;
ktime_t now, delta;
if (!ts->tick_stopped)
return;
/* Update jiffies first */
now = ktime_get();
ktime_t now;
local_irq_disable();
tick_nohz_stop_idle(cpu);
if (!ts->tick_stopped) {
local_irq_enable();
return;
}
/* Update jiffies first */
select_nohz_load_balancer(0);
now = ktime_get();
tick_do_update_jiffies64(now);
cpu_clear(cpu, nohz_cpu_mask);
/* Account the idle time */
delta = ktime_sub(now, ts->idle_entrytime);
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
/*
* We stopped the tick in idle. Update process times would miss the
* time we slept as update_process_times does only a 1 tick