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/* int_latency_bench.c - interrupt latency benchmark support */
/*
* Copyright (c) 2012-2015 Wind River Systems, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "toolchain.h"
#include "sections.h"
#include <stdint.h> /* uint32_t */
#include <limits.h> /* ULONG_MAX */
#include <misc/printk.h> /* printk */
#include <sys_clock.h>
#include <drivers/system_timer.h>
#define NB_CACHE_WARMING_DRY_RUN 7
/*
* Timestamp corresponding to when interrupt were turned off.
* A value of zero indicated interrupt are not currently locked.
*/
static uint32_t int_locked_timestamp;
/* stats tracking the minimum and maximum time when interrupts were locked */
static uint32_t int_locked_latency_min = ULONG_MAX;
static uint32_t int_locked_latency_max;
/* overhead added to intLock/intUnlock by this latency benchmark */
static uint32_t initial_start_delay;
static uint32_t nesting_delay;
static uint32_t stop_delay;
/* counter tracking intLock/intUnlock calls once interrupt are locked */
static uint32_t int_lock_unlock_nest;
/* indicate if the interrupt latency benchamrk is ready to be used */
static uint32_t int_latency_bench_ready;
/* min amount of time it takes from HW interrupt generation to 'C' handler */
uint32_t _hw_irq_to_c_handler_latency = ULONG_MAX;
/**
*
* @brief Start tracking time spent with interrupts locked
*
* calls to lock interrupt can nest, so this routine can be called numerous
* times before interrupt are unlocked
*
* @return N/A
*
*/
void _int_latency_start(void)
{
/* when interrupts are not already locked, take time stamp */
if (!int_locked_timestamp && int_latency_bench_ready) {
int_locked_timestamp = sys_cycle_get_32();
int_lock_unlock_nest = 0;
}
int_lock_unlock_nest++;
}
/**
*
* @brief Stop accumulating time spent for when interrupts are locked
*
* This is only call once when the interrupt are being reenabled
*
* @return N/A
*
*/
void _int_latency_stop(void)
{
uint32_t delta;
uint32_t delayOverhead;
uint32_t currentTime = sys_cycle_get_32();
/* ensured intLatencyStart() was invoked first */
if (int_locked_timestamp) {
/*
* time spent with interrupt lock is:
* (current time - time when interrupt got disabled first) -
* (delay when invoking start + number nested calls to intLock *
* time it takes to call intLatencyStart + intLatencyStop)
*/
delta = (currentTime - int_locked_timestamp);
/*
* Substract overhead introduce by the int latency benchmark
* only if
* it is bigger than delta. It can be possible sometimes for
* delta to
* be smaller than the estimated overhead.
*/
delayOverhead =
(initial_start_delay +
((int_lock_unlock_nest - 1) * nesting_delay) + stop_delay);
if (delta >= delayOverhead)
delta -= delayOverhead;
/* update max */
if (delta > int_locked_latency_max)
int_locked_latency_max = delta;
/* update min */
if (delta < int_locked_latency_min)
int_locked_latency_min = delta;
/* interrupts are now enabled, get ready for next interrupt lock
*/
int_locked_timestamp = 0;
}
}
/**
*
* @brief Initialize interrupt latency benchmark
*
* @return N/A
*
*/
void int_latency_init(void)
{
uint32_t timeToReadTime;
uint32_t cacheWarming = NB_CACHE_WARMING_DRY_RUN;
int_latency_bench_ready = 1;
/*
* measuring delay introduced by the interrupt latency benchmark few
* times to ensure we get the best possible values. The overhead of
* invoking the latency can changes runtime (i.e. cache hit or miss)
* but an estimated overhead is used to adjust Max interrupt latency.
* The overhead introduced by benchmark is composed of three values:
* initial_start_delay, nesting_delay, stop_delay.
*/
while (cacheWarming) {
/* measure how much time it takes to read time */
timeToReadTime = sys_cycle_get_32();
timeToReadTime = sys_cycle_get_32() - timeToReadTime;
/* measure time to call intLatencyStart() and intLatencyStop
* takes
*/
initial_start_delay = sys_cycle_get_32();
_int_latency_start();
initial_start_delay =
sys_cycle_get_32() - initial_start_delay - timeToReadTime;
nesting_delay = sys_cycle_get_32();
_int_latency_start();
nesting_delay = sys_cycle_get_32() - nesting_delay - timeToReadTime;
stop_delay = sys_cycle_get_32();
_int_latency_stop();
stop_delay = sys_cycle_get_32() - stop_delay - timeToReadTime;
/* re-initialize globals to default values */
int_locked_latency_min = ULONG_MAX;
int_locked_latency_max = 0;
cacheWarming--;
}
}
/**
*
* @brief Dumps interrupt latency values
*
* The interrupt latency value measures
*
* @return N/A
*
*/
void int_latency_show(void)
{
uint32_t intHandlerLatency = 0;
if (!int_latency_bench_ready) {
printk("error: int_latency_init() has not been invoked\n");
return;
}
if (int_locked_latency_min != ULONG_MAX) {
if (_hw_irq_to_c_handler_latency == ULONG_MAX) {
intHandlerLatency = 0;
printk(" Min latency from hw interrupt up to 'C' int. "
"handler: "
"not measured\n");
} else {
intHandlerLatency = _hw_irq_to_c_handler_latency;
printk(" Min latency from hw interrupt up to 'C' int. "
"handler:"
" %d tcs = %d nsec\n",
intHandlerLatency,
SYS_CLOCK_HW_CYCLES_TO_NS(intHandlerLatency));
}
printk(" Max interrupt latency (includes hw int. to 'C' "
"handler):"
" %d tcs = %d nsec\n",
int_locked_latency_max + intHandlerLatency,
SYS_CLOCK_HW_CYCLES_TO_NS(int_locked_latency_max + intHandlerLatency));
printk(" Overhead substracted from Max int. latency:\n"
" for int. lock : %d tcs = %d nsec\n"
" each time int. lock nest: %d tcs = %d nsec\n"
" for int. unlocked : %d tcs = %d nsec\n",
initial_start_delay,
SYS_CLOCK_HW_CYCLES_TO_NS(initial_start_delay),
nesting_delay,
SYS_CLOCK_HW_CYCLES_TO_NS(nesting_delay),
stop_delay,
SYS_CLOCK_HW_CYCLES_TO_NS(stop_delay));
} else {
printk("interrupts were not locked and unlocked yet\n");
}
/*
* Lets start with new values so that one extra long path executed
* with interrupt disabled hide smaller paths with interrupt
* disabled.
*/
int_locked_latency_min = ULONG_MAX;
int_locked_latency_max = 0;
}