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
30 #include <lttng/ust-clock.h>
33 * For sake of example, transform time into a coarse clock (freq: 1KHz).
34 * Note that division can be slow on some architectures. Should be
35 * avoided. Use shift and multiplication instead. e.g.:
37 * Operation: / 1000000ULL
38 * 1/1000000ULL = .000001
39 * 2^19 < 1000000 < 2^20
40 * Add a 10 bits shift to increase accuracy:
41 * 2^(19+10) = 536870912
42 * x * 1 / 2^(19+10) ~= .000001
43 * 537 * 1 / 2^29 = .00000100024044513702
44 * 537 (multiplication factor) is between 2^9 and 2^10.
46 * In order not to overflow, first right shift by 10, multiply, and right
49 #define DIV_CLOCK_SHIFT1 10
50 #define DIV_CLOCK_MUL 537
51 #define DIV_CLOCK_SHIFT2 19
54 uint64_t plugin_read64(void)
58 clock_gettime(CLOCK_MONOTONIC
, &ts
);
60 * This is a rather dumb example, but it illustrates the plugin
61 * mechanism: we take the monotonic clock, and transform it into
62 * a very coarse clock, which increment only at 1KHz frequency.
64 return ((uint64_t) ts
.tv_sec
* 1000ULL)
65 + ((DIV_CLOCK_MUL
* ((uint64_t) ts
.tv_nsec
>> DIV_CLOCK_SHIFT1
))
70 uint64_t plugin_freq(void)
72 return 1000; /* 1KHz clock (very coarse!) */
76 int plugin_uuid(char *uuid
)
78 const char myuuid
[] = "123456789012345678901234567890123456";
81 * Should read some unique identifier for this clock shared
82 * across all components of the system using this clock for
85 memcpy(uuid
, myuuid
, LTTNG_UST_UUID_STR_LEN
);
90 const char *plugin_name(void)
92 return "my_example_clock";
96 const char *plugin_description(void)
98 return "Coarse monotonic clock at 1KHz";
101 void lttng_ust_clock_plugin_init(void)
105 ret
= lttng_ust_trace_clock_set_read64_cb(plugin_read64
);
107 fprintf(stderr
, "Error setting clock override read64 callback: %s\n",
111 ret
= lttng_ust_trace_clock_set_freq_cb(plugin_freq
);
113 fprintf(stderr
, "Error setting clock override freq callback: %s\n",
117 ret
= lttng_ust_trace_clock_set_uuid_cb(plugin_uuid
);
119 fprintf(stderr
, "Error setting clock override uuid callback: %s\n",
124 ret
= lttng_ust_trace_clock_set_name_cb(plugin_name
);
126 fprintf(stderr
, "Error setting clock override name callback: %s\n",
131 ret
= lttng_ust_trace_clock_set_description_cb(plugin_description
);
133 fprintf(stderr
, "Error setting clock override description callback: %s\n",
138 ret
= lttng_ust_enable_trace_clock_override();
140 fprintf(stderr
, "Error enabling clock override: %s\n",
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