1 #include <linux/delay.h>
2 #include <linux/module.h>
3 #include <linux/kthread.h>
4 #include <linux/trace_clock.h>
6 #define CREATE_TRACE_POINTS
7 #include "trace_benchmark.h"
9 static struct task_struct *bm_event_thread;
11 static char bm_str[BENCHMARK_EVENT_STRLEN] = "START";
14 static u64 bm_totalsq;
21 static unsigned int bm_avg;
22 static unsigned int bm_std;
24 static bool ok_to_run;
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.
36 static void trace_do_benchmark(void)
47 /* Only run if the tracepoint is actually active */
48 if (!trace_benchmark_event_enabled() || !tracing_is_on())
52 start = trace_clock_local();
53 trace_benchmark_event(bm_str);
54 stop = trace_clock_local();
62 * The first read is cold cached, keep it separate from the
67 scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
68 "first=%llu [COLD CACHED]", bm_first);
76 if (!bm_min || delta < bm_min)
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.
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);
92 bm_totalsq += delta * delta;
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)
100 stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total;
101 do_div(stddev, (u32)bm_cnt);
102 do_div(stddev, (u32)bm_cnt - 1);
107 do_div(delta, bm_cnt);
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.
120 * Where N is the squared number to find the square
129 do_div(seed, last_seed);
132 } while (i++ < 10 && last_seed != seed);
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);
146 static int benchmark_event_kthread(void *arg)
148 /* sleep a bit to make sure the tracepoint gets activated */
151 while (!kthread_should_stop()) {
153 trace_do_benchmark();
156 * We don't go to sleep, but let others
166 * When the benchmark tracepoint is enabled, it calls this
167 * function and the thread that calls the tracepoint is created.
169 int trace_benchmark_reg(void)
172 pr_warning("trace benchmark cannot be started via kernel command line\n");
176 bm_event_thread = kthread_run(benchmark_event_kthread,
177 NULL, "event_benchmark");
178 if (IS_ERR(bm_event_thread)) {
179 pr_warning("trace benchmark failed to create kernel thread\n");
180 return PTR_ERR(bm_event_thread);
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.
191 void trace_benchmark_unreg(void)
193 if (!bm_event_thread)
196 kthread_stop(bm_event_thread);
197 bm_event_thread = NULL;
199 strcpy(bm_str, "START");
206 /* These don't need to be reset but reset them anyway */
213 static __init int ok_to_run_trace_benchmark(void)
220 early_initcall(ok_to_run_trace_benchmark);