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x86, bts, ftrace: a BTS ftrace plug-in prototype

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Impact: add new ftrace plugin

A prototype for a BTS ftrace plug-in.

The tracer collects branch trace in a cyclic buffer for each cpu.

The tracer is not configurable and the trace for each snapshot is
appended when doing cat /debug/tracing/trace.

This is a proof of concept that will be extended with future patches
to become a (hopefully) useful tool.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Markus Metzger 2008-11-25 09:24:15 +01:00 • committed by Ingo Molnar
commit 1e9b51c283
5 changed files with 301 additions and 0 deletions
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1
arch/x86/Kconfig.cpu
View file

@ -515,6 +515,7 @@ config CPU_SUP_UMC_32
config X86_DS
def_bool X86_PTRACE_BTS
depends on X86_DEBUGCTLMSR
select HAVE_HW_BRANCH_TRACER
config X86_PTRACE_BTS
bool "Branch Trace Store"

11
kernel/trace/Kconfig
View file

@ -28,6 +28,9 @@ config HAVE_DYNAMIC_FTRACE
config HAVE_FTRACE_MCOUNT_RECORD
bool
config HAVE_HW_BRANCH_TRACER
bool
config TRACER_MAX_TRACE
bool
@ -233,6 +236,14 @@ config STACK_TRACER
Say N if unsure.
config BTS_TRACER
depends on HAVE_HW_BRANCH_TRACER
bool "Trace branches"
select TRACING
help
This tracer records all branches on the system in a circular
buffer giving access to the last N branches for each cpu.
config DYNAMIC_FTRACE
bool "enable/disable ftrace tracepoints dynamically"
depends on FUNCTION_TRACER

1
kernel/trace/Makefile
View file

@ -31,5 +31,6 @@ obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
obj-$(CONFIG_BOOT_TRACER) += trace_boot.o
obj-$(CONFIG_FUNCTION_RET_TRACER) += trace_functions_return.o
obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
obj-$(CONFIG_BTS_TRACER) += trace_bts.o
libftrace-y := ftrace.o

12
kernel/trace/trace.h
View file

@ -27,6 +27,7 @@ enum trace_type {
TRACE_BOOT_RET,
TRACE_FN_RET,
TRACE_USER_STACK,
TRACE_BTS,
__TRACE_LAST_TYPE
};
@ -153,6 +154,12 @@ struct trace_branch {
char correct;
};
struct bts_entry {
struct trace_entry ent;
unsigned long from;
unsigned long to;
};
/*
* trace_flag_type is an enumeration that holds different
* states when a trace occurs. These are:
@ -258,6 +265,7 @@ extern void __ftrace_bad_type(void);
IF_ASSIGN(var, ent, struct trace_boot_ret, TRACE_BOOT_RET);\
IF_ASSIGN(var, ent, struct trace_branch, TRACE_BRANCH); \
IF_ASSIGN(var, ent, struct ftrace_ret_entry, TRACE_FN_RET);\
IF_ASSIGN(var, ent, struct bts_entry, TRACE_BTS);\
__ftrace_bad_type(); \
} while (0)
@ -392,6 +400,10 @@ void trace_function(struct trace_array *tr,
void
trace_function_return(struct ftrace_retfunc *trace);
void trace_bts(struct trace_array *tr,
unsigned long from,
unsigned long to);
void tracing_start_cmdline_record(void);
void tracing_stop_cmdline_record(void);
void tracing_sched_switch_assign_trace(struct trace_array *tr);

276
kernel/trace/trace_bts.c Normal file
View file

@ -0,0 +1,276 @@
/*
* BTS tracer
*
* Copyright (C) 2008 Markus Metzger <markus.t.metzger@gmail.com>
*
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/debugfs.h>
#include <linux/ftrace.h>
#include <linux/kallsyms.h>
#include <asm/ds.h>
#include "trace.h"
#define SIZEOF_BTS (1 << 13)
static DEFINE_PER_CPU(struct bts_tracer *, tracer);
static DEFINE_PER_CPU(unsigned char[SIZEOF_BTS], buffer);
#define this_tracer per_cpu(tracer, smp_processor_id())
#define this_buffer per_cpu(buffer, smp_processor_id())
/*
* Information to interpret a BTS record.
* This will go into an in-kernel BTS interface.
*/
static unsigned char sizeof_field;
static unsigned long debugctl_mask;
#define sizeof_bts (3 * sizeof_field)
static void bts_trace_cpuinit(struct cpuinfo_x86 *c)
{
switch (c->x86) {
case 0x6:
switch (c->x86_model) {
case 0x0 ... 0xC:
break;
case 0xD:
case 0xE: /* Pentium M */
sizeof_field = sizeof(long);
debugctl_mask = (1<<6)|(1<<7);
break;
default:
sizeof_field = 8;
debugctl_mask = (1<<6)|(1<<7);
break;
}
break;
case 0xF:
switch (c->x86_model) {
case 0x0:
case 0x1:
case 0x2: /* Netburst */
sizeof_field = sizeof(long);
debugctl_mask = (1<<2)|(1<<3);
break;
default:
/* sorry, don't know about them */
break;
}
break;
default:
/* sorry, don't know about them */
break;
}
}
static inline void bts_enable(void)
{
unsigned long debugctl;
rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl | debugctl_mask);
}
static inline void bts_disable(void)
{
unsigned long debugctl;
rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl & ~debugctl_mask);
}
static void bts_trace_reset(struct trace_array *tr)
{
int cpu;
tr->time_start = ftrace_now(tr->cpu);
for_each_online_cpu(cpu)
tracing_reset(tr, cpu);
}
static void bts_trace_start_cpu(void *arg)
{
this_tracer =
ds_request_bts(/* task = */ NULL, this_buffer, SIZEOF_BTS,
/* ovfl = */ NULL, /* th = */ (size_t)-1);
if (IS_ERR(this_tracer)) {
this_tracer = NULL;
return;
}
bts_enable();
}
static void bts_trace_start(struct trace_array *tr)
{
int cpu;
bts_trace_reset(tr);
for_each_cpu_mask(cpu, cpu_possible_map)
smp_call_function_single(cpu, bts_trace_start_cpu, NULL, 1);
}
static void bts_trace_stop_cpu(void *arg)
{
if (this_tracer) {
bts_disable();
ds_release_bts(this_tracer);
this_tracer = NULL;
}
}
static void bts_trace_stop(struct trace_array *tr)
{
int cpu;
for_each_cpu_mask(cpu, cpu_possible_map)
smp_call_function_single(cpu, bts_trace_stop_cpu, NULL, 1);
}
static int bts_trace_init(struct trace_array *tr)
{
bts_trace_cpuinit(&boot_cpu_data);
bts_trace_reset(tr);
bts_trace_start(tr);
return 0;
}
static void bts_trace_print_header(struct seq_file *m)
{
#ifdef __i386__
seq_puts(m, "# CPU# FROM TO FUNCTION\n");
seq_puts(m, "# | | | |\n");
#else
seq_puts(m,
"# CPU# FROM TO FUNCTION\n");
seq_puts(m,
"# | | | |\n");
#endif
}
static enum print_line_t bts_trace_print_line(struct trace_iterator *iter)
{
struct trace_entry *entry = iter->ent;
struct trace_seq *seq = &iter->seq;
struct bts_entry *it;
trace_assign_type(it, entry);
if (entry->type == TRACE_BTS) {
int ret;
#ifdef CONFIG_KALLSYMS
char function[KSYM_SYMBOL_LEN];
sprint_symbol(function, it->from);
#else
char *function = "<unknown>";
#endif
ret = trace_seq_printf(seq, "%4d 0x%lx -> 0x%lx [%s]\n",
entry->cpu, it->from, it->to, function);
if (!ret)
return TRACE_TYPE_PARTIAL_LINE;;
return TRACE_TYPE_HANDLED;
}
return TRACE_TYPE_UNHANDLED;
}
void trace_bts(struct trace_array *tr, unsigned long from, unsigned long to)
{
struct ring_buffer_event *event;
struct bts_entry *entry;
unsigned long irq;
event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry), &irq);
if (!event)
return;
entry = ring_buffer_event_data(event);
tracing_generic_entry_update(&entry->ent, 0, from);
entry->ent.type = TRACE_BTS;
entry->ent.cpu = smp_processor_id();
entry->from = from;
entry->to = to;
ring_buffer_unlock_commit(tr->buffer, event, irq);
}
static void trace_bts_at(struct trace_array *tr, size_t index)
{
const void *raw = NULL;
unsigned long from, to;
int err;
err = ds_access_bts(this_tracer, index, &raw);
if (err < 0)
return;
from = *(const unsigned long *)raw;
to = *(const unsigned long *)((const char *)raw + sizeof_field);
trace_bts(tr, from, to);
}
static void trace_bts_cpu(void *arg)
{
struct trace_array *tr = (struct trace_array *) arg;
size_t index = 0, end = 0, i;
int err;
if (!this_tracer)
return;
bts_disable();
err = ds_get_bts_index(this_tracer, &index);
if (err < 0)
goto out;
err = ds_get_bts_end(this_tracer, &end);
if (err < 0)
goto out;
for (i = index; i < end; i++)
trace_bts_at(tr, i);
for (i = 0; i < index; i++)
trace_bts_at(tr, i);
out:
bts_enable();
}
static void trace_bts_prepare(struct trace_iterator *iter)
{
int cpu;
for_each_cpu_mask(cpu, cpu_possible_map)
smp_call_function_single(cpu, trace_bts_cpu, iter->tr, 1);
}
struct tracer bts_tracer __read_mostly =
{
.name = "bts",
.init = bts_trace_init,
.reset = bts_trace_stop,
.print_header = bts_trace_print_header,
.print_line = bts_trace_print_line,
.start = bts_trace_start,
.stop = bts_trace_stop,
.open = trace_bts_prepare
};
__init static int init_bts_trace(void)
{
return register_tracer(&bts_tracer);
}
device_initcall(init_bts_trace);