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/*
* arch/mips/kernel/trace-clock.c
*
* Trace clock for mips.
*
* Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>, October 2008
*/
#include <linux/module.h>
#include <linux/trace-clock.h>
#include <linux/jiffies.h>
#include <linux/timer.h>
#include <linux/spinlock.h>
static u64 trace_clock_last_tsc;
static DEFINE_PER_CPU(struct timer_list, update_timer);
static DEFINE_SPINLOCK(async_tsc_lock);
static int async_tsc_refcount; /* Number of readers */
static int async_tsc_enabled; /* Async TSC enabled on all online CPUs */
/*
* Support for architectures with non-sync TSCs.
* When the local TSC is discovered to lag behind the highest TSC counter, we
* increment the TSC count of an amount that should be, ideally, lower than the
* execution time of this routine, in cycles : this is the granularity we look
* for : we must be able to order the events.
*/
#if BITS_PER_LONG == 64
notrace u64 trace_clock_async_tsc_read(void)
{
u64 new_tsc, last_tsc;
WARN_ON(!async_tsc_refcount || !async_tsc_enabled);
new_tsc = trace_clock_read_synthetic_tsc();
do {
last_tsc = trace_clock_last_tsc;
if (new_tsc < last_tsc)
new_tsc = last_tsc + TRACE_CLOCK_MIN_PROBE_DURATION;
/*
* If cmpxchg fails with a value higher than the new_tsc, don't
* retry : the value has been incremented and the events
* happened almost at the same time.
* We must retry if cmpxchg fails with a lower value :
* it means that we are the CPU with highest frequency and
* therefore MUST update the value.
*/
} while (cmpxchg64(&trace_clock_last_tsc, last_tsc, new_tsc) < new_tsc);
return new_tsc;
}
EXPORT_SYMBOL_GPL(trace_clock_async_tsc_read);
#else
/*
* Emulate an atomic 64-bits update with a spinlock.
* Note : preempt_disable or irq save must be explicit with raw_spinlock_t.
* Given we use a spinlock for this time base, we should never be called from
* NMI context.
*/
static raw_spinlock_t trace_clock_lock =
(raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
static inline u64 trace_clock_cmpxchg64(u64 *ptr, u64 old, u64 new)
{
u64 val;
val = *ptr;
if (likely(val == old))
*ptr = val = new;
return val;
}
notrace u64 trace_clock_async_tsc_read(void)
{
u64 new_tsc, last_tsc;
unsigned long flags;
WARN_ON(!async_tsc_refcount || !async_tsc_enabled);
local_irq_save(flags);
__raw_spin_lock(&trace_clock_lock);
new_tsc = trace_clock_read_synthetic_tsc();
do {
last_tsc = trace_clock_last_tsc;
if (new_tsc < last_tsc)
new_tsc = last_tsc + TRACE_CLOCK_MIN_PROBE_DURATION;
/*
* If cmpxchg fails with a value higher than the new_tsc, don't
* retry : the value has been incremented and the events
* happened almost at the same time.
* We must retry if cmpxchg fails with a lower value :
* it means that we are the CPU with highest frequency and
* therefore MUST update the value.
*/
} while (trace_clock_cmpxchg64(&trace_clock_last_tsc, last_tsc,
new_tsc) < new_tsc);
__raw_spin_unlock(&trace_clock_lock);
local_irq_restore(flags);
return new_tsc;
}
EXPORT_SYMBOL_GPL(trace_clock_async_tsc_read);
#endif
static void update_timer_ipi(void *info)
{
(void)trace_clock_async_tsc_read();
}
/*
* update_timer_fct : - Timer function to resync the clocks
* @data: unused
*
* Fires every jiffy.
*/
static void update_timer_fct(unsigned long data)
{
(void)trace_clock_async_tsc_read();
per_cpu(update_timer, smp_processor_id()).expires = jiffies + 1;
add_timer_on(&per_cpu(update_timer, smp_processor_id()),
smp_processor_id());
}
static void enable_trace_clock(int cpu)
{
init_timer(&per_cpu(update_timer, cpu));
per_cpu(update_timer, cpu).function = update_timer_fct;
per_cpu(update_timer, cpu).expires = jiffies + 1;
smp_call_function_single(cpu, update_timer_ipi, NULL, 1);
add_timer_on(&per_cpu(update_timer, cpu), cpu);
}
static void disable_trace_clock(int cpu)
{
del_timer_sync(&per_cpu(update_timer, cpu));
}
void get_trace_clock(void)
{
int cpu;
get_synthetic_tsc();
spin_lock(&async_tsc_lock);
if (async_tsc_refcount++ || tsc_is_sync())
goto end;
async_tsc_enabled = 1;
for_each_online_cpu(cpu)
enable_trace_clock(cpu);
end:
spin_unlock(&async_tsc_lock);
}
EXPORT_SYMBOL_GPL(get_trace_clock);
void put_trace_clock(void)
{
int cpu;
spin_lock(&async_tsc_lock);
WARN_ON(async_tsc_refcount <= 0);
if (async_tsc_refcount != 1 || !async_tsc_enabled)
goto end;
for_each_online_cpu(cpu)
disable_trace_clock(cpu);
async_tsc_enabled = 0;
end:
async_tsc_refcount--;
spin_unlock(&async_tsc_lock);
put_synthetic_tsc();
}
EXPORT_SYMBOL_GPL(put_trace_clock);
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