2 * lttng-clock-override-example.c
4 * Copyright (c) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to deal
8 * in the Software without restriction, including without limitation the rights
9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10 * copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
29 #include <lttng/ust-clock.h>
32 * For sake of example, transform time into a coarse clock (freq: 1KHz).
33 * Note that division can be slow on some architectures. Should be
34 * avoided. Use shift and multiplication instead. e.g.:
36 * Operation: / 1000000ULL
37 * 1/1000000ULL = .000001
38 * 2^19 < 1000000 < 2^20
39 * Add a 10 bits shift to increase accuracy:
40 * 2^(19+10) = 536870912
41 * x * 1 / 2^(19+10) ~= .000001
42 * 537 * 1 / 2^29 = .00000100024044513702
43 * 537 (multiplication factor) is between 2^9 and 2^10.
45 * In order not to overflow, first right shift by 10, multiply, and right
48 #define DIV_CLOCK_SHIFT1 10
49 #define DIV_CLOCK_MUL 537
50 #define DIV_CLOCK_SHIFT2 19
53 uint64_t plugin_read64(void)
57 clock_gettime(CLOCK_MONOTONIC
, &ts
);
59 * This is a rather dumb example, but it illustrates the plugin
60 * mechanism: we take the monotonic clock, and transform it into
61 * a very coarse clock, which increment only at 1KHz frequency.
63 return ((uint64_t) ts
.tv_sec
* 1000ULL)
64 + ((DIV_CLOCK_MUL
* ((uint64_t) ts
.tv_nsec
>> DIV_CLOCK_SHIFT1
))
69 uint64_t plugin_freq(void)
71 return 1000; /* 1KHz clock (very coarse!) */
75 int plugin_uuid(char *uuid
)
77 const char myuuid
[] = "123456789012345678901234567890123456";
80 * Should read some unique identifier for this clock shared
81 * across all components of the system using this clock for
84 memcpy(uuid
, myuuid
, LTTNG_UST_UUID_STR_LEN
);
89 const char *plugin_name(void)
91 return "my_example_clock";
95 const char *plugin_description(void)
97 return "Coarse monotonic clock at 1KHz";
100 void lttng_ust_clock_plugin_init(void)
104 ret
= lttng_ust_trace_clock_set_read64_cb(plugin_read64
);
106 fprintf(stderr
, "Error setting clock override read64 callback: %s\n",
110 ret
= lttng_ust_trace_clock_set_freq_cb(plugin_freq
);
112 fprintf(stderr
, "Error setting clock override freq callback: %s\n",
116 ret
= lttng_ust_trace_clock_set_uuid_cb(plugin_uuid
);
118 fprintf(stderr
, "Error setting clock override uuid callback: %s\n",
123 ret
= lttng_ust_trace_clock_set_name_cb(plugin_name
);
125 fprintf(stderr
, "Error setting clock override name callback: %s\n",
130 ret
= lttng_ust_trace_clock_set_description_cb(plugin_description
);
132 fprintf(stderr
, "Error setting clock override description callback: %s\n",
137 ret
= lttng_ust_enable_trace_clock_override();
139 fprintf(stderr
, "Error enabling clock override: %s\n",
This page took 0.031624 seconds and 4 git commands to generate.