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![Chunyan Zhang](/assets/img/avatar_default.png)
There's no need to record the time tracepoints take when tracing is off. This is because: 1) We cannot see these records since ring_buffer record is off at that moment. 2) If tracing is off and benchmark tracepoint is enabled, the time tracepoint takes is fewer than the same situation when tracing is on, since the tracepoints need to be wrote into ring_buffer, it would take more time. If turn on tracing at this moment, the average and standard deviation cannot exactly present the time that tracepoints take to write data into ring_buffer. Link: http://lkml.kernel.org/r/1445947933-27955-1-git-send-email-zhang.chunyan@linaro.org Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
198 lines
4.3 KiB
C
198 lines
4.3 KiB
C
#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/kthread.h>
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#include <linux/trace_clock.h>
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#define CREATE_TRACE_POINTS
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#include "trace_benchmark.h"
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static struct task_struct *bm_event_thread;
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static char bm_str[BENCHMARK_EVENT_STRLEN] = "START";
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static u64 bm_total;
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static u64 bm_totalsq;
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static u64 bm_last;
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static u64 bm_max;
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static u64 bm_min;
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static u64 bm_first;
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static u64 bm_cnt;
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static u64 bm_stddev;
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static unsigned int bm_avg;
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static unsigned int bm_std;
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/*
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* This gets called in a loop recording the time it took to write
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* the tracepoint. What it writes is the time statistics of the last
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* tracepoint write. As there is nothing to write the first time
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* it simply writes "START". As the first write is cold cache and
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* the rest is hot, we save off that time in bm_first and it is
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* reported as "first", which is shown in the second write to the
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* tracepoint. The "first" field is writen within the statics from
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* then on but never changes.
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*/
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static void trace_do_benchmark(void)
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{
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u64 start;
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u64 stop;
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u64 delta;
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u64 stddev;
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u64 seed;
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u64 last_seed;
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unsigned int avg;
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unsigned int std = 0;
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/* Only run if the tracepoint is actually active */
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if (!trace_benchmark_event_enabled() || !tracing_is_on())
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return;
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local_irq_disable();
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start = trace_clock_local();
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trace_benchmark_event(bm_str);
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stop = trace_clock_local();
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local_irq_enable();
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bm_cnt++;
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delta = stop - start;
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/*
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* The first read is cold cached, keep it separate from the
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* other calculations.
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*/
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if (bm_cnt == 1) {
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bm_first = delta;
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scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
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"first=%llu [COLD CACHED]", bm_first);
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return;
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}
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bm_last = delta;
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if (delta > bm_max)
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bm_max = delta;
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if (!bm_min || delta < bm_min)
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bm_min = delta;
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/*
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* When bm_cnt is greater than UINT_MAX, it breaks the statistics
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* accounting. Freeze the statistics when that happens.
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* We should have enough data for the avg and stddev anyway.
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*/
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if (bm_cnt > UINT_MAX) {
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scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
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"last=%llu first=%llu max=%llu min=%llu ** avg=%u std=%d std^2=%lld",
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bm_last, bm_first, bm_max, bm_min, bm_avg, bm_std, bm_stddev);
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return;
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}
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bm_total += delta;
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bm_totalsq += delta * delta;
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if (bm_cnt > 1) {
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/*
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* Apply Welford's method to calculate standard deviation:
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* s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
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*/
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stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total;
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do_div(stddev, (u32)bm_cnt);
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do_div(stddev, (u32)bm_cnt - 1);
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} else
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stddev = 0;
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delta = bm_total;
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do_div(delta, bm_cnt);
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avg = delta;
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if (stddev > 0) {
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int i = 0;
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/*
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* stddev is the square of standard deviation but
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* we want the actualy number. Use the average
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* as our seed to find the std.
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*
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* The next try is:
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* x = (x + N/x) / 2
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*
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* Where N is the squared number to find the square
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* root of.
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*/
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seed = avg;
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do {
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last_seed = seed;
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seed = stddev;
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if (!last_seed)
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break;
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do_div(seed, last_seed);
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seed += last_seed;
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do_div(seed, 2);
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} while (i++ < 10 && last_seed != seed);
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std = seed;
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}
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scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
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"last=%llu first=%llu max=%llu min=%llu avg=%u std=%d std^2=%lld",
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bm_last, bm_first, bm_max, bm_min, avg, std, stddev);
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bm_std = std;
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bm_avg = avg;
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bm_stddev = stddev;
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}
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static int benchmark_event_kthread(void *arg)
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{
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/* sleep a bit to make sure the tracepoint gets activated */
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msleep(100);
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while (!kthread_should_stop()) {
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trace_do_benchmark();
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/*
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* We don't go to sleep, but let others
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* run as well.
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*/
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cond_resched();
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}
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return 0;
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}
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/*
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* When the benchmark tracepoint is enabled, it calls this
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* function and the thread that calls the tracepoint is created.
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*/
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void trace_benchmark_reg(void)
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{
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bm_event_thread = kthread_run(benchmark_event_kthread,
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NULL, "event_benchmark");
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WARN_ON(!bm_event_thread);
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}
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/*
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* When the benchmark tracepoint is disabled, it calls this
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* function and the thread that calls the tracepoint is deleted
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* and all the numbers are reset.
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*/
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void trace_benchmark_unreg(void)
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{
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if (!bm_event_thread)
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return;
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kthread_stop(bm_event_thread);
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strcpy(bm_str, "START");
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bm_total = 0;
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bm_totalsq = 0;
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bm_last = 0;
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bm_max = 0;
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bm_min = 0;
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bm_cnt = 0;
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/* These don't need to be reset but reset them anyway */
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bm_first = 0;
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bm_std = 0;
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bm_avg = 0;
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bm_stddev = 0;
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}
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