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[PATCH] improve precision of idle time detection.

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Increase the precision of the idle time calculation that is exported
to user space via /sys/devices/system/cpu/cpu<x>/idle_time_us

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2008-12-31 15:11:40 +01:00
parent aa5e97ce4b
commit 6f43092441
4 changed files with 62 additions and 38 deletions
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69
arch/s390/kernel/process.c
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@ -38,6 +38,7 @@
#include <linux/utsname.h>
#include <linux/tick.h>
#include <linux/elfcore.h>
#include <linux/kernel_stat.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/system.h>
@ -79,30 +80,19 @@ DEFINE_PER_CPU(struct s390_idle_data, s390_idle) = {
.lock = __SPIN_LOCK_UNLOCKED(s390_idle.lock)
};
static int s390_idle_enter(void)
{
struct s390_idle_data *idle;
idle = &__get_cpu_var(s390_idle);
spin_lock(&idle->lock);
idle->idle_count++;
idle->in_idle = 1;
idle->idle_enter = get_clock();
spin_unlock(&idle->lock);
vtime_stop_cpu_timer();
return NOTIFY_OK;
}
void s390_idle_leave(void)
{
struct s390_idle_data *idle;
unsigned long long idle_time;
vtime_start_cpu_timer();
idle = &__get_cpu_var(s390_idle);
idle_time = S390_lowcore.int_clock - idle->idle_enter;
spin_lock(&idle->lock);
idle->idle_time += get_clock() - idle->idle_enter;
idle->in_idle = 0;
idle->idle_time += idle_time;
idle->idle_enter = 0ULL;
idle->idle_count++;
spin_unlock(&idle->lock);
vtime_start_cpu_timer();
}
extern void s390_handle_mcck(void);
@ -111,16 +101,16 @@ extern void s390_handle_mcck(void);
*/
static void default_idle(void)
{
struct s390_idle_data *idle = &__get_cpu_var(s390_idle);
unsigned long addr;
psw_t psw;
/* CPU is going idle. */
local_irq_disable();
if (need_resched()) {
local_irq_enable();
return;
}
if (s390_idle_enter() == NOTIFY_BAD) {
local_irq_enable();
return;
}
#ifdef CONFIG_HOTPLUG_CPU
if (cpu_is_offline(smp_processor_id())) {
preempt_enable_no_resched();
@ -138,9 +128,42 @@ static void default_idle(void)
trace_hardirqs_on();
/* Don't trace preempt off for idle. */
stop_critical_timings();
vtime_stop_cpu_timer();
/*
* The inline assembly is equivalent to
* idle->idle_enter = get_clock();
* __load_psw_mask(psw_kernel_bits | PSW_MASK_WAIT |
* PSW_MASK_IO | PSW_MASK_EXT);
* The difference is that the inline assembly makes sure that
* the stck instruction is right before the lpsw instruction.
* This is done to increase the precision.
*/
/* Wait for external, I/O or machine check interrupt. */
__load_psw_mask(psw_kernel_bits | PSW_MASK_WAIT |
PSW_MASK_IO | PSW_MASK_EXT);
psw.mask = psw_kernel_bits|PSW_MASK_WAIT|PSW_MASK_IO|PSW_MASK_EXT;
#ifndef __s390x__
asm volatile(
" basr %0,0\n"
"0: ahi %0,1f-0b\n"
" st %0,4(%2)\n"
" stck 0(%3)\n"
" lpsw 0(%2)\n"
"1:"
: "=&d" (addr), "=m" (idle->idle_enter)
: "a" (&psw), "a" (&idle->idle_enter), "m" (psw)
: "memory", "cc");
#else /* __s390x__ */
asm volatile(
" larl %0,1f\n"
" stg %0,8(%2)\n"
" stck 0(%3)\n"
" lpswe 0(%2)\n"
"1:"
: "=&d" (addr), "=m" (idle->idle_enter)
: "a" (&psw), "a" (&idle->idle_enter), "m" (psw)
: "memory", "cc");
#endif /* __s390x__ */
start_critical_timings();
}