1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
|
/* int_latency_bench.c - interrupt latency benchmark support */
/*
* Copyright (c) 2012-2015 Wind River Systems, Inc.
*
* SPDX-License-Identifier: Apache-2.0
*/
#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;
}
|
