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Commit 1e9b51c2 authored by Markus Metzger's avatar Markus Metzger Committed by Ingo Molnar
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x86, bts, ftrace: a BTS ftrace plug-in prototype 



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: default avatarMarkus Metzger <markus.t.metzger@intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 8bba1bf5

arch/x86/Kconfig.cpu

+1 −0
Original line number Diff line number Diff line
@@ -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"

kernel/trace/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -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

kernel/trace/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -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

kernel/trace/trace.h

+12 −0
Original line number Diff line number Diff line
@@ -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);

kernel/trace/trace_bts.c

0 → 100644
+276 −0
Original line number Diff line number Diff line 
/*

 * 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);