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81dc9f0e SRRH |
1 | #include <linux/delay.h> |
2 | #include <linux/module.h> | |
3 | #include <linux/kthread.h> | |
4 | #include <linux/trace_clock.h> | |
5 | ||
6 | #define CREATE_TRACE_POINTS | |
7 | #include "trace_benchmark.h" | |
8 | ||
9 | static struct task_struct *bm_event_thread; | |
10 | ||
11 | static char bm_str[BENCHMARK_EVENT_STRLEN] = "START"; | |
12 | ||
13 | static u64 bm_total; | |
14 | static u64 bm_totalsq; | |
15 | static u64 bm_last; | |
16 | static u64 bm_max; | |
17 | static u64 bm_min; | |
18 | static u64 bm_first; | |
34839f5a SRRH |
19 | static u64 bm_cnt; |
20 | static u64 bm_stddev; | |
21 | static unsigned int bm_avg; | |
22 | static unsigned int bm_std; | |
81dc9f0e | 23 | |
9c1f6bb8 SRRH |
24 | static bool ok_to_run; |
25 | ||
81dc9f0e SRRH |
26 | /* |
27 | * This gets called in a loop recording the time it took to write | |
28 | * the tracepoint. What it writes is the time statistics of the last | |
29 | * tracepoint write. As there is nothing to write the first time | |
30 | * it simply writes "START". As the first write is cold cache and | |
31 | * the rest is hot, we save off that time in bm_first and it is | |
32 | * reported as "first", which is shown in the second write to the | |
33 | * tracepoint. The "first" field is writen within the statics from | |
34 | * then on but never changes. | |
35 | */ | |
36 | static void trace_do_benchmark(void) | |
37 | { | |
38 | u64 start; | |
39 | u64 stop; | |
40 | u64 delta; | |
72e2fe38 | 41 | u64 stddev; |
81dc9f0e | 42 | u64 seed; |
81dc9f0e SRRH |
43 | u64 last_seed; |
44 | unsigned int avg; | |
45 | unsigned int std = 0; | |
46 | ||
47 | /* Only run if the tracepoint is actually active */ | |
bdb5d0f9 | 48 | if (!trace_benchmark_event_enabled() || !tracing_is_on()) |
81dc9f0e SRRH |
49 | return; |
50 | ||
51 | local_irq_disable(); | |
52 | start = trace_clock_local(); | |
53 | trace_benchmark_event(bm_str); | |
54 | stop = trace_clock_local(); | |
55 | local_irq_enable(); | |
56 | ||
57 | bm_cnt++; | |
58 | ||
59 | delta = stop - start; | |
60 | ||
61 | /* | |
62 | * The first read is cold cached, keep it separate from the | |
63 | * other calculations. | |
64 | */ | |
65 | if (bm_cnt == 1) { | |
66 | bm_first = delta; | |
67 | scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, | |
68 | "first=%llu [COLD CACHED]", bm_first); | |
69 | return; | |
70 | } | |
71 | ||
72 | bm_last = delta; | |
73 | ||
81dc9f0e SRRH |
74 | if (delta > bm_max) |
75 | bm_max = delta; | |
76 | if (!bm_min || delta < bm_min) | |
77 | bm_min = delta; | |
78 | ||
34839f5a SRRH |
79 | /* |
80 | * When bm_cnt is greater than UINT_MAX, it breaks the statistics | |
81 | * accounting. Freeze the statistics when that happens. | |
82 | * We should have enough data for the avg and stddev anyway. | |
83 | */ | |
84 | if (bm_cnt > UINT_MAX) { | |
85 | scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, | |
86 | "last=%llu first=%llu max=%llu min=%llu ** avg=%u std=%d std^2=%lld", | |
87 | bm_last, bm_first, bm_max, bm_min, bm_avg, bm_std, bm_stddev); | |
88 | return; | |
89 | } | |
90 | ||
91 | bm_total += delta; | |
92 | bm_totalsq += delta * delta; | |
93 | ||
94 | ||
81dc9f0e SRRH |
95 | if (bm_cnt > 1) { |
96 | /* | |
97 | * Apply Welford's method to calculate standard deviation: | |
98 | * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) | |
99 | */ | |
100 | stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total; | |
34839f5a SRRH |
101 | do_div(stddev, (u32)bm_cnt); |
102 | do_div(stddev, (u32)bm_cnt - 1); | |
81dc9f0e SRRH |
103 | } else |
104 | stddev = 0; | |
105 | ||
106 | delta = bm_total; | |
107 | do_div(delta, bm_cnt); | |
108 | avg = delta; | |
109 | ||
110 | if (stddev > 0) { | |
111 | int i = 0; | |
112 | /* | |
113 | * stddev is the square of standard deviation but | |
114 | * we want the actualy number. Use the average | |
115 | * as our seed to find the std. | |
116 | * | |
117 | * The next try is: | |
118 | * x = (x + N/x) / 2 | |
119 | * | |
120 | * Where N is the squared number to find the square | |
121 | * root of. | |
122 | */ | |
123 | seed = avg; | |
124 | do { | |
125 | last_seed = seed; | |
126 | seed = stddev; | |
127 | if (!last_seed) | |
128 | break; | |
129 | do_div(seed, last_seed); | |
130 | seed += last_seed; | |
131 | do_div(seed, 2); | |
132 | } while (i++ < 10 && last_seed != seed); | |
133 | ||
134 | std = seed; | |
135 | } | |
136 | ||
137 | scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, | |
138 | "last=%llu first=%llu max=%llu min=%llu avg=%u std=%d std^2=%lld", | |
139 | bm_last, bm_first, bm_max, bm_min, avg, std, stddev); | |
34839f5a SRRH |
140 | |
141 | bm_std = std; | |
142 | bm_avg = avg; | |
143 | bm_stddev = stddev; | |
81dc9f0e SRRH |
144 | } |
145 | ||
146 | static int benchmark_event_kthread(void *arg) | |
147 | { | |
148 | /* sleep a bit to make sure the tracepoint gets activated */ | |
149 | msleep(100); | |
150 | ||
151 | while (!kthread_should_stop()) { | |
152 | ||
153 | trace_do_benchmark(); | |
154 | ||
155 | /* | |
156 | * We don't go to sleep, but let others | |
157 | * run as well. | |
158 | */ | |
159 | cond_resched(); | |
160 | } | |
161 | ||
162 | return 0; | |
163 | } | |
164 | ||
165 | /* | |
166 | * When the benchmark tracepoint is enabled, it calls this | |
167 | * function and the thread that calls the tracepoint is created. | |
168 | */ | |
8cf868af | 169 | int trace_benchmark_reg(void) |
81dc9f0e | 170 | { |
9c1f6bb8 | 171 | if (!ok_to_run) { |
1dd349ab SRRH |
172 | pr_warning("trace benchmark cannot be started via kernel command line\n"); |
173 | return -EBUSY; | |
174 | } | |
175 | ||
81dc9f0e SRRH |
176 | bm_event_thread = kthread_run(benchmark_event_kthread, |
177 | NULL, "event_benchmark"); | |
1dd349ab SRRH |
178 | if (!bm_event_thread) { |
179 | pr_warning("trace benchmark failed to create kernel thread\n"); | |
180 | return -ENOMEM; | |
181 | } | |
182 | ||
8cf868af | 183 | return 0; |
81dc9f0e SRRH |
184 | } |
185 | ||
186 | /* | |
187 | * When the benchmark tracepoint is disabled, it calls this | |
188 | * function and the thread that calls the tracepoint is deleted | |
189 | * and all the numbers are reset. | |
190 | */ | |
191 | void trace_benchmark_unreg(void) | |
192 | { | |
193 | if (!bm_event_thread) | |
194 | return; | |
195 | ||
196 | kthread_stop(bm_event_thread); | |
1dd349ab | 197 | bm_event_thread = NULL; |
81dc9f0e SRRH |
198 | |
199 | strcpy(bm_str, "START"); | |
200 | bm_total = 0; | |
201 | bm_totalsq = 0; | |
202 | bm_last = 0; | |
203 | bm_max = 0; | |
204 | bm_min = 0; | |
205 | bm_cnt = 0; | |
34839f5a | 206 | /* These don't need to be reset but reset them anyway */ |
81dc9f0e | 207 | bm_first = 0; |
34839f5a SRRH |
208 | bm_std = 0; |
209 | bm_avg = 0; | |
210 | bm_stddev = 0; | |
81dc9f0e | 211 | } |
9c1f6bb8 SRRH |
212 | |
213 | static __init int ok_to_run_trace_benchmark(void) | |
214 | { | |
215 | ok_to_run = true; | |
216 | ||
217 | return 0; | |
218 | } | |
219 | ||
220 | early_initcall(ok_to_run_trace_benchmark); |