kernel/trace/trace_branch.c

// SPDX-License-Identifier: GPL-2.0
/*
 * unlikely profiler
 *
 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
 */
#include <linux/kallsyms.h>
#include <linux/seq_file.h>
#include <linux/spinlock.h>
#include <linux/irqflags.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ftrace.h>
#include <linux/hash.h>
#include <linux/fs.h>
#include <asm/local.h>

#include "trace.h"
#include "trace_stat.h"
#include "trace_output.h"

#ifdef CONFIG_BRANCH_TRACER

static struct tracer branch_trace;
static int branch_tracing_enabled __read_mostly;
static DEFINE_MUTEX(branch_tracing_mutex);

static struct trace_array *branch_tracer;

static void
probe_likely_condition(struct ftrace_likely_data *f, int val, int expect)
{
	struct trace_event_call *call = &event_branch;
	struct trace_array *tr = branch_tracer;
	struct trace_buffer *buffer;
	struct trace_array_cpu *data;
	struct ring_buffer_event *event;
	struct trace_branch *entry;
	unsigned long flags;
	unsigned int trace_ctx;
	const char *p;

	if (current->trace_recursion & TRACE_BRANCH_BIT)
		return;

	/*
	 * I would love to save just the ftrace_likely_data pointer, but
	 * this code can also be used by modules. Ugly things can happen
	 * if the module is unloaded, and then we go and read the
	 * pointer.  This is slower, but much safer.
	 */

	if (unlikely(!tr))
		return;

	raw_local_irq_save(flags);
	current->trace_recursion |= TRACE_BRANCH_BIT;
	data = this_cpu_ptr(tr->array_buffer.data);
	if (atomic_read(&data->disabled))
		goto out;

	trace_ctx = tracing_gen_ctx_flags(flags);
	buffer = tr->array_buffer.buffer;
	event = trace_buffer_lock_reserve(buffer, TRACE_BRANCH,
					  sizeof(*entry), trace_ctx);
	if (!event)
		goto out;

	entry	= ring_buffer_event_data(event);

	/* Strip off the path, only save the file */
	p = f->data.file + strlen(f->data.file);
	while (p >= f->data.file && *p != '/')
		p--;
	p++;

	strncpy(entry->func, f->data.func, TRACE_FUNC_SIZE);
	strncpy(entry->file, p, TRACE_FILE_SIZE);
	entry->func[TRACE_FUNC_SIZE] = 0;
	entry->file[TRACE_FILE_SIZE] = 0;
	entry->constant = f->constant;
	entry->line = f->data.line;
	entry->correct = val == expect;

	if (!call_filter_check_discard(call, entry, buffer, event))
		trace_buffer_unlock_commit_nostack(buffer, event);

 out:
	current->trace_recursion &= ~TRACE_BRANCH_BIT;
	raw_local_irq_restore(flags);
}

static inline
void trace_likely_condition(struct ftrace_likely_data *f, int val, int expect)
{
	if (!branch_tracing_enabled)
		return;

	probe_likely_condition(f, val, expect);
}

int enable_branch_tracing(struct trace_array *tr)
{
	mutex_lock(&branch_tracing_mutex);
	branch_tracer = tr;
	/*
	 * Must be seen before enabling. The reader is a condition
	 * where we do not need a matching rmb()
	 */
	smp_wmb();
	branch_tracing_enabled++;
	mutex_unlock(&branch_tracing_mutex);

	return 0;
}

void disable_branch_tracing(void)
{
	mutex_lock(&branch_tracing_mutex);

	if (!branch_tracing_enabled)
		goto out_unlock;

	branch_tracing_enabled--;

 out_unlock:
	mutex_unlock(&branch_tracing_mutex);
}

static int branch_trace_init(struct trace_array *tr)
{
	return enable_branch_tracing(tr);
}

static void branch_trace_reset(struct trace_array *tr)
{
	disable_branch_tracing();
}

static enum print_line_t trace_branch_print(struct trace_iterator *iter,
					    int flags, struct trace_event *event)
{
	struct trace_branch *field;

	trace_assign_type(field, iter->ent);

	trace_seq_printf(&iter->seq, "[%s] %s:%s:%d\n",
			 field->correct ? "  ok  " : " MISS ",
			 field->func,
			 field->file,
			 field->line);

	return trace_handle_return(&iter->seq);
}

static void branch_print_header(struct seq_file *s)
{
	seq_puts(s, "#           TASK-PID    CPU#    TIMESTAMP  CORRECT"
		    "  FUNC:FILE:LINE\n"
		    "#              | |       |          |         |   "
		    "    |\n");
}

static struct trace_event_functions trace_branch_funcs = {
	.trace		= trace_branch_print,
};

static struct trace_event trace_branch_event = {
	.type		= TRACE_BRANCH,
	.funcs		= &trace_branch_funcs,
};

static struct tracer branch_trace __read_mostly =
{
	.name		= "branch",
	.init		= branch_trace_init,
	.reset		= branch_trace_reset,
#ifdef CONFIG_FTRACE_SELFTEST
	.selftest	= trace_selftest_startup_branch,
#endif /* CONFIG_FTRACE_SELFTEST */
	.print_header	= branch_print_header,
};

__init static int init_branch_tracer(void)
{
	int ret;

	ret = register_trace_event(&trace_branch_event);
	if (!ret) {
		printk(KERN_WARNING "Warning: could not register "
				    "branch events\n");
		return 1;
	}
	return register_tracer(&branch_trace);
}
core_initcall(init_branch_tracer);

#else
static inline
void trace_likely_condition(struct ftrace_likely_data *f, int val, int expect)
{
}
#endif /* CONFIG_BRANCH_TRACER */

void ftrace_likely_update(struct ftrace_likely_data *f, int val,
			  int expect, int is_constant)
{
	unsigned long flags = user_access_save();

	/* A constant is always correct */
	if (is_constant) {
		f->constant++;
		val = expect;
	}
	/*
	 * I would love to have a trace point here instead, but the
	 * trace point code is so inundated with unlikely and likely
	 * conditions that the recursive nightmare that exists is too
	 * much to try to get working. At least for now.
	 */
	trace_likely_condition(f, val, expect);

	/* FIXME: Make this atomic! */
	if (val == expect)
		f->data.correct++;
	else
		f->data.incorrect++;

	user_access_restore(flags);
}
EXPORT_SYMBOL(ftrace_likely_update);

extern unsigned long __start_annotated_branch_profile[];
extern unsigned long __stop_annotated_branch_profile[];

static int annotated_branch_stat_headers(struct seq_file *m)
{
	seq_puts(m, " correct incorrect  % "
		    "       Function                "
		    "  File              Line\n"
		    " ------- ---------  - "
		    "       --------                "
		    "  ----              ----\n");
	return 0;
}

static inline long get_incorrect_percent(const struct ftrace_branch_data *p)
{
	long percent;

	if (p->correct) {
		percent = p->incorrect * 100;
		percent /= p->correct + p->incorrect;
	} else
		percent = p->incorrect ? 100 : -1;

	return percent;
}

static const char *branch_stat_process_file(struct ftrace_branch_data *p)
{
	const char *f;

	/* Only print the file, not the path */
	f = p->file + strlen(p->file);
	while (f >= p->file && *f != '/')
		f--;
	return ++f;
}

static void branch_stat_show(struct seq_file *m,
			     struct ftrace_branch_data *p, const char *f)
{
	long percent;

	/*
	 * The miss is overlayed on correct, and hit on incorrect.
	 */
	percent = get_incorrect_percent(p);

	if (percent < 0)
		seq_puts(m, "  X ");
	else
		seq_printf(m, "%3ld ", percent);

	seq_printf(m, "%-30.30s %-20.20s %d\n", p->func, f, p->line);
}

static int branch_stat_show_normal(struct seq_file *m,
				   struct ftrace_branch_data *p, const char *f)
{
	seq_printf(m, "%8lu %8lu ",  p->correct, p->incorrect);
	branch_stat_show(m, p, f);
	return 0;
}

static int annotate_branch_stat_show(struct seq_file *m, void *v)
{
	struct ftrace_likely_data *p = v;
	const char *f;
	int l;

	f = branch_stat_process_file(&p->data);

	if (!p->constant)
		return branch_stat_show_normal(m, &p->data, f);

	l = snprintf(NULL, 0, "/%lu", p->constant);
	l = l > 8 ? 0 : 8 - l;

	seq_printf(m, "%8lu/%lu %*lu ",
		   p->data.correct, p->constant, l, p->data.incorrect);
	branch_stat_show(m, &p->data, f);
	return 0;
}

static void *annotated_branch_stat_start(struct tracer_stat *trace)
{
	return __start_annotated_branch_profile;
}

static void *
annotated_branch_stat_next(void *v, int idx)
{
	struct ftrace_likely_data *p = v;

	++p;

	if ((void *)p >= (void *)__stop_annotated_branch_profile)
		return NULL;

	return p;
}

static int annotated_branch_stat_cmp(const void *p1, const void *p2)
{
	const struct ftrace_branch_data *a = p1;
	const struct ftrace_branch_data *b = p2;

	long percent_a, percent_b;

	percent_a = get_incorrect_percent(a);
	percent_b = get_incorrect_percent(b);

	if (percent_a < percent_b)
		return -1;
	if (percent_a > percent_b)
		return 1;

	if (a->incorrect < b->incorrect)
		return -1;
	if (a->incorrect > b->incorrect)
		return 1;

	/*
	 * Since the above shows worse (incorrect) cases
	 * first, we continue that by showing best (correct)
	 * cases last.
	 */
	if (a->correct > b->correct)
		return -1;
	if (a->correct < b->correct)
		return 1;

	return 0;
}

static struct tracer_stat annotated_branch_stats = {
	.name = "branch_annotated",
	.stat_start = annotated_branch_stat_start,
	.stat_next = annotated_branch_stat_next,
	.stat_cmp = annotated_branch_stat_cmp,
	.stat_headers = annotated_branch_stat_headers,
	.stat_show = annotate_branch_stat_show
};

__init static int init_annotated_branch_stats(void)
{
	int ret;

	ret = register_stat_tracer(&annotated_branch_stats);
	if (!ret) {
		printk(KERN_WARNING "Warning: could not register "
				    "annotated branches stats\n");
		return 1;
	}
	return 0;
}
fs_initcall(init_annotated_branch_stats);

#ifdef CONFIG_PROFILE_ALL_BRANCHES

extern unsigned long __start_branch_profile[];
extern unsigned long __stop_branch_profile[];

static int all_branch_stat_headers(struct seq_file *m)
{
	seq_puts(m, "   miss      hit    % "
		    "       Function                "
		    "  File              Line\n"
		    " ------- ---------  - "
		    "       --------                "
		    "  ----              ----\n");
	return 0;
}

static void *all_branch_stat_start(struct tracer_stat *trace)
{
	return __start_branch_profile;
}

static void *
all_branch_stat_next(void *v, int idx)
{
	struct ftrace_branch_data *p = v;

	++p;

	if ((void *)p >= (void *)__stop_branch_profile)
		return NULL;

	return p;
}

static int all_branch_stat_show(struct seq_file *m, void *v)
{
	struct ftrace_branch_data *p = v;
	const char *f;

	f = branch_stat_process_file(p);
	return branch_stat_show_normal(m, p, f);
}

static struct tracer_stat all_branch_stats = {
	.name = "branch_all",
	.stat_start = all_branch_stat_start,
	.stat_next = all_branch_stat_next,
	.stat_headers = all_branch_stat_headers,
	.stat_show = all_branch_stat_show
};

__init static int all_annotated_branch_stats(void)
{
	int ret;

	ret = register_stat_tracer(&all_branch_stats);
	if (!ret) {
		printk(KERN_WARNING "Warning: could not register "
				    "all branches stats\n");
		return 1;
	}
	return 0;
}
fs_initcall(all_annotated_branch_stats);
#endif /* CONFIG_PROFILE_ALL_BRANCHES */