kernel/trace/trace_benchmark.c

Source file repositories/reference/linux-study-clean/kernel/trace/trace_benchmark.c

File Facts

System
Linux kernel
Corpus path
kernel/trace/trace_benchmark.c
Extension
.c
Size
5354 bytes
Lines
229
Domain
Core OS
Bucket
Scheduler, Processes, Timers, Sync, And Syscalls
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/trace_clock.h>

#define CREATE_TRACE_POINTS
#include "trace_benchmark.h"

static struct task_struct *bm_event_thread;

static char bm_str[BENCHMARK_EVENT_STRLEN] = "START";

static u64 bm_total;
static u64 bm_totalsq;
static u64 bm_last;
static u64 bm_max;
static u64 bm_min;
static u64 bm_first;
static u64 bm_cnt;
static u64 bm_stddev;
static unsigned int bm_avg;
static unsigned int bm_std;

static bool ok_to_run;

/*
 * This gets called in a loop recording the time it took to write
 * the tracepoint. What it writes is the time statistics of the last
 * tracepoint write. As there is nothing to write the first time
 * it simply writes "START". As the first write is cold cache and
 * the rest is hot, we save off that time in bm_first and it is
 * reported as "first", which is shown in the second write to the
 * tracepoint. The "first" field is written within the statics from
 * then on but never changes.
 */
static void trace_do_benchmark(void)
{
	u64 start;
	u64 stop;
	u64 delta;
	u64 stddev;
	u64 seed;
	u64 last_seed;
	unsigned int avg;
	unsigned int std = 0;

	/* Only run if the tracepoint is actually active */
	if (!trace_benchmark_event_enabled() || !tracing_is_on())
		return;

	local_irq_disable();
	start = trace_clock_local();
	trace_benchmark_event(bm_str, bm_last);
	stop = trace_clock_local();
	local_irq_enable();

	bm_cnt++;

	delta = stop - start;

	/*
	 * The first read is cold cached, keep it separate from the
	 * other calculations.
	 */
	if (bm_cnt == 1) {
		bm_first = delta;
		scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
			  "first=%llu [COLD CACHED]", bm_first);
		return;
	}

	bm_last = delta;

	if (delta > bm_max)
		bm_max = delta;
	if (!bm_min || delta < bm_min)
		bm_min = delta;

	/*
	 * When bm_cnt is greater than UINT_MAX, it breaks the statistics
	 * accounting. Freeze the statistics when that happens.
	 * We should have enough data for the avg and stddev anyway.
	 */
	if (bm_cnt > UINT_MAX) {
		scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
		    "last=%llu first=%llu max=%llu min=%llu ** avg=%u std=%d std^2=%lld",
			  bm_last, bm_first, bm_max, bm_min, bm_avg, bm_std, bm_stddev);
		return;
	}

Annotation

Implementation Notes