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b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
81dc9f0e SRRH |
2 | #include <linux/delay.h> |
3 | #include <linux/module.h> | |
4 | #include <linux/kthread.h> | |
5 | #include <linux/trace_clock.h> | |
6 | ||
7 | #define CREATE_TRACE_POINTS | |
8 | #include "trace_benchmark.h" | |
9 | ||
10 | static struct task_struct *bm_event_thread; | |
11 | ||
12 | static char bm_str[BENCHMARK_EVENT_STRLEN] = "START"; | |
13 | ||
14 | static u64 bm_total; | |
15 | static u64 bm_totalsq; | |
16 | static u64 bm_last; | |
17 | static u64 bm_max; | |
18 | static u64 bm_min; | |
19 | static u64 bm_first; | |
34839f5a SRRH |
20 | static u64 bm_cnt; |
21 | static u64 bm_stddev; | |
22 | static unsigned int bm_avg; | |
23 | static unsigned int bm_std; | |
81dc9f0e | 24 | |
9c1f6bb8 SRRH |
25 | static bool ok_to_run; |
26 | ||
81dc9f0e SRRH |
27 | /* |
28 | * This gets called in a loop recording the time it took to write | |
29 | * the tracepoint. What it writes is the time statistics of the last | |
30 | * tracepoint write. As there is nothing to write the first time | |
31 | * it simply writes "START". As the first write is cold cache and | |
32 | * the rest is hot, we save off that time in bm_first and it is | |
33 | * reported as "first", which is shown in the second write to the | |
34 | * tracepoint. The "first" field is writen within the statics from | |
35 | * then on but never changes. | |
36 | */ | |
37 | static void trace_do_benchmark(void) | |
38 | { | |
39 | u64 start; | |
40 | u64 stop; | |
41 | u64 delta; | |
72e2fe38 | 42 | u64 stddev; |
81dc9f0e | 43 | u64 seed; |
81dc9f0e SRRH |
44 | u64 last_seed; |
45 | unsigned int avg; | |
46 | unsigned int std = 0; | |
47 | ||
48 | /* Only run if the tracepoint is actually active */ | |
bdb5d0f9 | 49 | if (!trace_benchmark_event_enabled() || !tracing_is_on()) |
81dc9f0e SRRH |
50 | return; |
51 | ||
52 | local_irq_disable(); | |
53 | start = trace_clock_local(); | |
54 | trace_benchmark_event(bm_str); | |
55 | stop = trace_clock_local(); | |
56 | local_irq_enable(); | |
57 | ||
58 | bm_cnt++; | |
59 | ||
60 | delta = stop - start; | |
61 | ||
62 | /* | |
63 | * The first read is cold cached, keep it separate from the | |
64 | * other calculations. | |
65 | */ | |
66 | if (bm_cnt == 1) { | |
67 | bm_first = delta; | |
68 | scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, | |
69 | "first=%llu [COLD CACHED]", bm_first); | |
70 | return; | |
71 | } | |
72 | ||
73 | bm_last = delta; | |
74 | ||
81dc9f0e SRRH |
75 | if (delta > bm_max) |
76 | bm_max = delta; | |
77 | if (!bm_min || delta < bm_min) | |
78 | bm_min = delta; | |
79 | ||
34839f5a SRRH |
80 | /* |
81 | * When bm_cnt is greater than UINT_MAX, it breaks the statistics | |
82 | * accounting. Freeze the statistics when that happens. | |
83 | * We should have enough data for the avg and stddev anyway. | |
84 | */ | |
85 | if (bm_cnt > UINT_MAX) { | |
86 | scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, | |
87 | "last=%llu first=%llu max=%llu min=%llu ** avg=%u std=%d std^2=%lld", | |
88 | bm_last, bm_first, bm_max, bm_min, bm_avg, bm_std, bm_stddev); | |
89 | return; | |
90 | } | |
91 | ||
92 | bm_total += delta; | |
93 | bm_totalsq += delta * delta; | |
94 | ||
95 | ||
81dc9f0e SRRH |
96 | if (bm_cnt > 1) { |
97 | /* | |
98 | * Apply Welford's method to calculate standard deviation: | |
99 | * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) | |
100 | */ | |
101 | stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total; | |
34839f5a SRRH |
102 | do_div(stddev, (u32)bm_cnt); |
103 | do_div(stddev, (u32)bm_cnt - 1); | |
81dc9f0e SRRH |
104 | } else |
105 | stddev = 0; | |
106 | ||
107 | delta = bm_total; | |
108 | do_div(delta, bm_cnt); | |
109 | avg = delta; | |
110 | ||
111 | if (stddev > 0) { | |
112 | int i = 0; | |
113 | /* | |
114 | * stddev is the square of standard deviation but | |
115 | * we want the actualy number. Use the average | |
116 | * as our seed to find the std. | |
117 | * | |
118 | * The next try is: | |
119 | * x = (x + N/x) / 2 | |
120 | * | |
121 | * Where N is the squared number to find the square | |
122 | * root of. | |
123 | */ | |
124 | seed = avg; | |
125 | do { | |
126 | last_seed = seed; | |
127 | seed = stddev; | |
128 | if (!last_seed) | |
129 | break; | |
130 | do_div(seed, last_seed); | |
131 | seed += last_seed; | |
132 | do_div(seed, 2); | |
133 | } while (i++ < 10 && last_seed != seed); | |
134 | ||
135 | std = seed; | |
136 | } | |
137 | ||
138 | scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, | |
139 | "last=%llu first=%llu max=%llu min=%llu avg=%u std=%d std^2=%lld", | |
140 | bm_last, bm_first, bm_max, bm_min, avg, std, stddev); | |
34839f5a SRRH |
141 | |
142 | bm_std = std; | |
143 | bm_avg = avg; | |
144 | bm_stddev = stddev; | |
81dc9f0e SRRH |
145 | } |
146 | ||
147 | static int benchmark_event_kthread(void *arg) | |
148 | { | |
149 | /* sleep a bit to make sure the tracepoint gets activated */ | |
150 | msleep(100); | |
151 | ||
152 | while (!kthread_should_stop()) { | |
153 | ||
154 | trace_do_benchmark(); | |
155 | ||
156 | /* | |
b980b117 SRV |
157 | * We don't go to sleep, but let others run as well. |
158 | * This is bascially a "yield()" to let any task that | |
159 | * wants to run, schedule in, but if the CPU is idle, | |
160 | * we'll keep burning cycles. | |
161 | * | |
162 | * Note the _rcu_qs() version of cond_resched() will | |
163 | * notify synchronize_rcu_tasks() that this thread has | |
164 | * passed a quiescent state for rcu_tasks. Otherwise | |
165 | * this thread will never voluntarily schedule which would | |
166 | * block synchronize_rcu_tasks() indefinitely. | |
81dc9f0e | 167 | */ |
e31d28b6 | 168 | cond_resched(); |
81dc9f0e SRRH |
169 | } |
170 | ||
171 | return 0; | |
172 | } | |
173 | ||
174 | /* | |
175 | * When the benchmark tracepoint is enabled, it calls this | |
176 | * function and the thread that calls the tracepoint is created. | |
177 | */ | |
8cf868af | 178 | int trace_benchmark_reg(void) |
81dc9f0e | 179 | { |
9c1f6bb8 | 180 | if (!ok_to_run) { |
1dd349ab SRRH |
181 | pr_warning("trace benchmark cannot be started via kernel command line\n"); |
182 | return -EBUSY; | |
183 | } | |
184 | ||
81dc9f0e SRRH |
185 | bm_event_thread = kthread_run(benchmark_event_kthread, |
186 | NULL, "event_benchmark"); | |
8f0994bb | 187 | if (IS_ERR(bm_event_thread)) { |
1dd349ab | 188 | pr_warning("trace benchmark failed to create kernel thread\n"); |
8f0994bb | 189 | return PTR_ERR(bm_event_thread); |
1dd349ab SRRH |
190 | } |
191 | ||
8cf868af | 192 | return 0; |
81dc9f0e SRRH |
193 | } |
194 | ||
195 | /* | |
196 | * When the benchmark tracepoint is disabled, it calls this | |
197 | * function and the thread that calls the tracepoint is deleted | |
198 | * and all the numbers are reset. | |
199 | */ | |
200 | void trace_benchmark_unreg(void) | |
201 | { | |
202 | if (!bm_event_thread) | |
203 | return; | |
204 | ||
205 | kthread_stop(bm_event_thread); | |
1dd349ab | 206 | bm_event_thread = NULL; |
81dc9f0e SRRH |
207 | |
208 | strcpy(bm_str, "START"); | |
209 | bm_total = 0; | |
210 | bm_totalsq = 0; | |
211 | bm_last = 0; | |
212 | bm_max = 0; | |
213 | bm_min = 0; | |
214 | bm_cnt = 0; | |
34839f5a | 215 | /* These don't need to be reset but reset them anyway */ |
81dc9f0e | 216 | bm_first = 0; |
34839f5a SRRH |
217 | bm_std = 0; |
218 | bm_avg = 0; | |
219 | bm_stddev = 0; | |
81dc9f0e | 220 | } |
9c1f6bb8 SRRH |
221 | |
222 | static __init int ok_to_run_trace_benchmark(void) | |
223 | { | |
224 | ok_to_run = true; | |
225 | ||
226 | return 0; | |
227 | } | |
228 | ||
229 | early_initcall(ok_to_run_trace_benchmark); |