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/* -*- linux-c -*-
* Counter aggregation Functions
* Copyright (C) 2005-2008 Red Hat Inc.
*
* This file is part of systemtap, and is free software. You can
* redistribute it and/or modify it under the terms of the GNU General
* Public License (GPL); either version 2, or (at your option) any
* later version.
*/
#ifndef _COUNTER_C_
#define _COUNTER_C_
/** @file counter.c
* @brief Counter Aggregation
*/
/** @addtogroup counter Counter Aggregation
* This is a 64-bit per-cpu Counter. It is much more efficient than an atomic counter
* because there is no contention between processors and caches in an SMP system. Use
* it when you want to count things and do not read the counter often. Ideally you
* should wait until probe exit time to read the Counter.
* @{
*/
/* This define will probably go away with the next checkin. */
/* locks are only here for testing */
#ifndef NEED_COUNTER_LOCKS
#define NEED_COUNTER_LOCKS 0
#endif
#if NEED_COUNTER_LOCKS == 1
#define COUNTER_LOCK(c) spin_lock(&c->lock)
#define COUNTER_UNLOCK(c) spin_unlock(&c->lock)
#else
#define COUNTER_LOCK(c) ;
#define COUNTER_UNLOCK(c) ;
#endif
struct _counter {
int64_t count;
#if NEED_COUNTER_LOCKS == 1
spinlock_t lock;
#endif
};
typedef struct _counter *Counter;
/** Initialize a Counter.
* Call this during probe initialization to create a Counter
*
* @return a Counter. Will be NULL on error.
*/
static Counter _stp_counter_init (void)
{
Counter cnt = _stp_alloc_percpu (struct _counter);
#if NEED_COUNTER_LOCKS == 1
{
int i;
stp_for_each_cpu(i) {
Counter c = per_cpu_ptr (cnt, i);
spin_lock_init(c->lock);
}
}
#endif
return cnt;
}
/** Add to a Counter.
* Adds an int64 to a Counter
*
* @param cnt Counter
* @param val int64 value
*/
static void _stp_counter_add (Counter cnt, int64_t val)
{
Counter c = per_cpu_ptr (cnt, get_cpu());
COUNTER_LOCK(c);
c->count += val;
COUNTER_UNLOCK(c);
put_cpu();
}
/** Get a Counter's per-cpu value.
* Get the value of a Counter for a specific CPU.
*
* @param cnt Counter
* @param cpu CPU number
* @param clear Set this to have the value cleared after reading.
* @return An int64 value.
*/
static int64_t _stp_counter_get_cpu (Counter cnt, int cpu, int clear)
{
int64_t val;
Counter c = per_cpu_ptr (cnt, cpu);
COUNTER_LOCK(c);
val = c->count;
if (clear)
c->count = 0;
COUNTER_UNLOCK(c);
return val;
}
/** Get a Counter's value.
* Get the value of a Counter. This is the sum of the counters for
* all CPUs. Because computing this sum requires reading all of the
* per-cpu values, doing it often will result in poor performance in
* multiprocessor systems.
*
* The clear parameter is intended for use in a polling situation when the
* values should be immediately cleared after reading.
* @param cnt Counter
* @param clear Set this to have the value cleared after reading.
* @return An int64 value.
*/
static int64_t _stp_counter_get (Counter cnt, int clear)
{
int i;
int64_t sum = 0;
stp_for_each_cpu(i) {
Counter c = per_cpu_ptr (cnt, i);
COUNTER_LOCK(c);
sum += c->count;
if (clear)
c->count = 0;
COUNTER_UNLOCK(c);
}
return sum;
}
/** Free a Counter.
* @param cnt Counter
*/
static void _stp_counter_free (Counter cnt)
{
_stp_free_percpu (cnt);
}
/** @} */
#undef COUNTER_LOCK
#undef COUNTER_UNLOCK
#endif /* _COUNTER_C_ */
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