drivers/oprofile/cpu_buffer.c - linux - Git at Google

 /**
  * @file cpu_buffer.c
  *
  * @remark Copyright 2002 OProfile authors
  * @remark Read the file COPYING
  *
  * @author John Levon <levon@movementarian.org>
  * @author Barry Kasindorf <barry.kasindorf@amd.com>
  *
  * Each CPU has a local buffer that stores PC value/event
  * pairs. We also log context switches when we notice them.
  * Eventually each CPU's buffer is processed into the global
  * event buffer by sync_buffer().
  *
  * We use a local buffer for two reasons: an NMI or similar
  * interrupt cannot synchronise, and high sampling rates
  * would lead to catastrophic global synchronisation if
  * a global buffer was used.
  */

 #include <linux/sched.h>
 #include <linux/oprofile.h>
 #include <linux/vmalloc.h>
 #include <linux/errno.h>

 #include "event_buffer.h"
 #include "cpu_buffer.h"
 #include "buffer_sync.h"
 #include "oprof.h"

 #define OP_BUFFER_FLAGS	0

 /*
  * Read and write access is using spin locking. Thus, writing to the
  * buffer by NMI handler (x86) could occur also during critical
  * sections when reading the buffer. To avoid this, there are 2
  * buffers for independent read and write access. Read access is in
  * process context only, write access only in the NMI handler. If the
  * read buffer runs empty, both buffers are swapped atomically. There
  * is potentially a small window during swapping where the buffers are
  * disabled and samples could be lost.
  *
  * Using 2 buffers is a little bit overhead, but the solution is clear
  * and does not require changes in the ring buffer implementation. It
  * can be changed to a single buffer solution when the ring buffer
  * access is implemented as non-locking atomic code.
  */
 static struct ring_buffer *op_ring_buffer_read;
 static struct ring_buffer *op_ring_buffer_write;
 DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);

 static void wq_sync_buffer(struct work_struct *work);

 #define DEFAULT_TIMER_EXPIRE (HZ / 10)
 static int work_enabled;

 unsigned long oprofile_get_cpu_buffer_size(void)
 {
 	return oprofile_cpu_buffer_size;
 }

 void oprofile_cpu_buffer_inc_smpl_lost(void)
 {
 	struct oprofile_cpu_buffer *cpu_buf
 		= &__get_cpu_var(cpu_buffer);

 	cpu_buf->sample_lost_overflow++;
 }

 void free_cpu_buffers(void)
 {
 	if (op_ring_buffer_read)
 		ring_buffer_free(op_ring_buffer_read);
 	op_ring_buffer_read = NULL;
 	if (op_ring_buffer_write)
 		ring_buffer_free(op_ring_buffer_write);
 	op_ring_buffer_write = NULL;
 }

 int alloc_cpu_buffers(void)
 {
 	int i;

 	unsigned long buffer_size = oprofile_cpu_buffer_size;

 	op_ring_buffer_read = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
 	if (!op_ring_buffer_read)
 		goto fail;
 	op_ring_buffer_write = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
 	if (!op_ring_buffer_write)
 		goto fail;

 	for_each_possible_cpu(i) {
 		struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

 		b->last_task = NULL;
 		b->last_is_kernel = -1;
 		b->tracing = 0;
 		b->buffer_size = buffer_size;
 		b->tail_pos = 0;
 		b->head_pos = 0;
 		b->sample_received = 0;
 		b->sample_lost_overflow = 0;
 		b->backtrace_aborted = 0;
 		b->sample_invalid_eip = 0;
 		b->cpu = i;
 		INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
 	}
 	return 0;

 fail:
 	free_cpu_buffers();
 	return -ENOMEM;
 }

 void start_cpu_work(void)
 {
 	int i;

 	work_enabled = 1;

 	for_each_online_cpu(i) {
 		struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

 		/*
 		 * Spread the work by 1 jiffy per cpu so they dont all
 		 * fire at once.
 		 */
 		schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
 	}
 }

 void end_cpu_work(void)
 {
 	int i;

 	work_enabled = 0;

 	for_each_online_cpu(i) {
 		struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

 		cancel_delayed_work(&b->work);
 	}

 	flush_scheduled_work();
 }

 int op_cpu_buffer_write_entry(struct op_entry *entry)
 {
 	entry->event = ring_buffer_lock_reserve(op_ring_buffer_write,
 						sizeof(struct op_sample),
 						&entry->irq_flags);
 	if (entry->event)
 		entry->sample = ring_buffer_event_data(entry->event);
 	else
 		entry->sample = NULL;

 	if (!entry->sample)
 		return -ENOMEM;

 	return 0;
 }

 int op_cpu_buffer_write_commit(struct op_entry *entry)
 {
 	return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event,
 					 entry->irq_flags);
 }

 struct op_sample *op_cpu_buffer_read_entry(int cpu)
 {
 	struct ring_buffer_event *e;
 	e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
 	if (e)
 		return ring_buffer_event_data(e);
 	if (ring_buffer_swap_cpu(op_ring_buffer_read,
 				 op_ring_buffer_write,
 				 cpu))
 		return NULL;
 	e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
 	if (e)
 		return ring_buffer_event_data(e);
 	return NULL;
 }

 unsigned long op_cpu_buffer_entries(int cpu)
 {
 	return ring_buffer_entries_cpu(op_ring_buffer_read, cpu)
 		+ ring_buffer_entries_cpu(op_ring_buffer_write, cpu);
 }

 static inline int
 add_sample(struct oprofile_cpu_buffer *cpu_buf,
 	   unsigned long pc, unsigned long event)
 {
 	struct op_entry entry;
 	int ret;

 	ret = op_cpu_buffer_write_entry(&entry);
 	if (ret)
 		return ret;

 	entry.sample->eip = pc;
 	entry.sample->event = event;

 	ret = op_cpu_buffer_write_commit(&entry);
 	if (ret)
 		return ret;

 	return 0;
 }

 static inline int
 add_code(struct oprofile_cpu_buffer *buffer, unsigned long value)
 {
 	return add_sample(buffer, ESCAPE_CODE, value);
 }

 /* This must be safe from any context. It's safe writing here
  * because of the head/tail separation of the writer and reader
  * of the CPU buffer.
  *
  * is_kernel is needed because on some architectures you cannot
  * tell if you are in kernel or user space simply by looking at
  * pc. We tag this in the buffer by generating kernel enter/exit
  * events whenever is_kernel changes
  */
 static int log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
 		      int is_kernel, unsigned long event)
 {
 	struct task_struct *task;

 	cpu_buf->sample_received++;

 	if (pc == ESCAPE_CODE) {
 		cpu_buf->sample_invalid_eip++;
 		return 0;
 	}

 	is_kernel = !!is_kernel;

 	task = current;

 	/* notice a switch from user->kernel or vice versa */
 	if (cpu_buf->last_is_kernel != is_kernel) {
 		cpu_buf->last_is_kernel = is_kernel;
 		if (add_code(cpu_buf, is_kernel))
 			goto fail;
 	}

 	/* notice a task switch */
 	if (cpu_buf->last_task != task) {
 		cpu_buf->last_task = task;
 		if (add_code(cpu_buf, (unsigned long)task))
 			goto fail;
 	}

 	if (add_sample(cpu_buf, pc, event))
 		goto fail;

 	return 1;

 fail:
 	cpu_buf->sample_lost_overflow++;
 	return 0;
 }

 static int oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
 {
 	add_code(cpu_buf, CPU_TRACE_BEGIN);
 	cpu_buf->tracing = 1;
 	return 1;
 }

 static void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
 {
 	cpu_buf->tracing = 0;
 }

 static inline void
 __oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 			  unsigned long event, int is_kernel)
 {
 	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);

 	if (!oprofile_backtrace_depth) {
 		log_sample(cpu_buf, pc, is_kernel, event);
 		return;
 	}

 	if (!oprofile_begin_trace(cpu_buf))
 		return;

 	/*
 	 * if log_sample() fail we can't backtrace since we lost the
 	 * source of this event
 	 */
 	if (log_sample(cpu_buf, pc, is_kernel, event))
 		oprofile_ops.backtrace(regs, oprofile_backtrace_depth);
 	oprofile_end_trace(cpu_buf);
 }

 void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 			     unsigned long event, int is_kernel)
 {
 	__oprofile_add_ext_sample(pc, regs, event, is_kernel);
 }

 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
 {
 	int is_kernel = !user_mode(regs);
 	unsigned long pc = profile_pc(regs);

 	__oprofile_add_ext_sample(pc, regs, event, is_kernel);
 }

 #ifdef CONFIG_OPROFILE_IBS

 #define MAX_IBS_SAMPLE_SIZE 14

 void oprofile_add_ibs_sample(struct pt_regs * const regs,
 			     unsigned int * const ibs_sample, int ibs_code)
 {
 	int is_kernel = !user_mode(regs);
 	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 	struct task_struct *task;
 	int fail = 0;

 	cpu_buf->sample_received++;

 	/* notice a switch from user->kernel or vice versa */
 	if (cpu_buf->last_is_kernel != is_kernel) {
 		if (add_code(cpu_buf, is_kernel))
 			goto fail;
 		cpu_buf->last_is_kernel = is_kernel;
 	}

 	/* notice a task switch */
 	if (!is_kernel) {
 		task = current;
 		if (cpu_buf->last_task != task) {
 			if (add_code(cpu_buf, (unsigned long)task))
 				goto fail;
 			cpu_buf->last_task = task;
 		}
 	}

 	fail = fail || add_code(cpu_buf, ibs_code);
 	fail = fail || add_sample(cpu_buf, ibs_sample[0], ibs_sample[1]);
 	fail = fail || add_sample(cpu_buf, ibs_sample[2], ibs_sample[3]);
 	fail = fail || add_sample(cpu_buf, ibs_sample[4], ibs_sample[5]);

 	if (ibs_code == IBS_OP_BEGIN) {
 		fail = fail || add_sample(cpu_buf, ibs_sample[6], ibs_sample[7]);
 		fail = fail || add_sample(cpu_buf, ibs_sample[8], ibs_sample[9]);
 		fail = fail || add_sample(cpu_buf, ibs_sample[10], ibs_sample[11]);
 	}

 	if (fail)
 		goto fail;

 	if (oprofile_backtrace_depth)
 		oprofile_ops.backtrace(regs, oprofile_backtrace_depth);

 	return;

 fail:
 	cpu_buf->sample_lost_overflow++;
 	return;
 }

 #endif

 void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
 {
 	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
 	log_sample(cpu_buf, pc, is_kernel, event);
 }

 void oprofile_add_trace(unsigned long pc)
 {
 	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);

 	if (!cpu_buf->tracing)
 		return;

 	/*
 	 * broken frame can give an eip with the same value as an
 	 * escape code, abort the trace if we get it
 	 */
 	if (pc == ESCAPE_CODE)
 		goto fail;

 	if (add_sample(cpu_buf, pc, 0))
 		goto fail;

 	return;
 fail:
 	cpu_buf->tracing = 0;
 	cpu_buf->backtrace_aborted++;
 	return;
 }

 /*
  * This serves to avoid cpu buffer overflow, and makes sure
  * the task mortuary progresses
  *
  * By using schedule_delayed_work_on and then schedule_delayed_work
  * we guarantee this will stay on the correct cpu
  */
 static void wq_sync_buffer(struct work_struct *work)
 {
 	struct oprofile_cpu_buffer *b =
 		container_of(work, struct oprofile_cpu_buffer, work.work);
 	if (b->cpu != smp_processor_id()) {
 		printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
 		       smp_processor_id(), b->cpu);

 		if (!cpu_online(b->cpu)) {
 			cancel_delayed_work(&b->work);
 			return;
 		}
 	}
 	sync_buffer(b->cpu);

 	/* don't re-add the work if we're shutting down */
 	if (work_enabled)
 		schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
 }
	/**
	* @file cpu_buffer.c
	*
	* @remark Copyright 2002 OProfile authors
	* @remark Read the file COPYING
	*
	* @author John Levon <levon@movementarian.org>
	* @author Barry Kasindorf <barry.kasindorf@amd.com>
	*
	* Each CPU has a local buffer that stores PC value/event
	* pairs. We also log context switches when we notice them.
	* Eventually each CPU's buffer is processed into the global
	* event buffer by sync_buffer().
	*
	* We use a local buffer for two reasons: an NMI or similar
	* interrupt cannot synchronise, and high sampling rates
	* would lead to catastrophic global synchronisation if
	* a global buffer was used.
	*/

	#include <linux/sched.h>
	#include <linux/oprofile.h>
	#include <linux/vmalloc.h>
	#include <linux/errno.h>

	#include "event_buffer.h"
	#include "cpu_buffer.h"
	#include "buffer_sync.h"
	#include "oprof.h"

	#define OP_BUFFER_FLAGS 0

	/*
	* Read and write access is using spin locking. Thus, writing to the
	* buffer by NMI handler (x86) could occur also during critical
	* sections when reading the buffer. To avoid this, there are 2
	* buffers for independent read and write access. Read access is in
	* process context only, write access only in the NMI handler. If the
	* read buffer runs empty, both buffers are swapped atomically. There
	* is potentially a small window during swapping where the buffers are
	* disabled and samples could be lost.
	*
	* Using 2 buffers is a little bit overhead, but the solution is clear
	* and does not require changes in the ring buffer implementation. It
	* can be changed to a single buffer solution when the ring buffer
	* access is implemented as non-locking atomic code.
	*/
	static struct ring_buffer *op_ring_buffer_read;
	static struct ring_buffer *op_ring_buffer_write;
	DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);

	static void wq_sync_buffer(struct work_struct *work);

	#define DEFAULT_TIMER_EXPIRE (HZ / 10)
	static int work_enabled;

	unsigned long oprofile_get_cpu_buffer_size(void)
	{
	return oprofile_cpu_buffer_size;
	}

	void oprofile_cpu_buffer_inc_smpl_lost(void)
	{
	struct oprofile_cpu_buffer *cpu_buf
	= &__get_cpu_var(cpu_buffer);

	cpu_buf->sample_lost_overflow++;
	}

	void free_cpu_buffers(void)
	{
	if (op_ring_buffer_read)
	ring_buffer_free(op_ring_buffer_read);
	op_ring_buffer_read = NULL;
	if (op_ring_buffer_write)
	ring_buffer_free(op_ring_buffer_write);
	op_ring_buffer_write = NULL;
	}

	int alloc_cpu_buffers(void)
	{
	int i;

	unsigned long buffer_size = oprofile_cpu_buffer_size;

	op_ring_buffer_read = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
	if (!op_ring_buffer_read)
	goto fail;
	op_ring_buffer_write = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
	if (!op_ring_buffer_write)
	goto fail;

	for_each_possible_cpu(i) {
	struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

	b->last_task = NULL;
	b->last_is_kernel = -1;
	b->tracing = 0;
	b->buffer_size = buffer_size;
	b->tail_pos = 0;
	b->head_pos = 0;
	b->sample_received = 0;
	b->sample_lost_overflow = 0;
	b->backtrace_aborted = 0;
	b->sample_invalid_eip = 0;
	b->cpu = i;
	INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
	}
	return 0;

	fail:
	free_cpu_buffers();
	return -ENOMEM;
	}

	void start_cpu_work(void)
	{
	int i;

	work_enabled = 1;

	for_each_online_cpu(i) {
	struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

	/*
	* Spread the work by 1 jiffy per cpu so they dont all
	* fire at once.
	*/
	schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
	}
	}

	void end_cpu_work(void)
	{
	int i;

	work_enabled = 0;

	for_each_online_cpu(i) {
	struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

	cancel_delayed_work(&b->work);
	}

	flush_scheduled_work();
	}

	int op_cpu_buffer_write_entry(struct op_entry *entry)
	{
	entry->event = ring_buffer_lock_reserve(op_ring_buffer_write,
	sizeof(struct op_sample),
	&entry->irq_flags);
	if (entry->event)
	entry->sample = ring_buffer_event_data(entry->event);
	else
	entry->sample = NULL;

	if (!entry->sample)
	return -ENOMEM;

	return 0;
	}

	int op_cpu_buffer_write_commit(struct op_entry *entry)
	{
	return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event,
	entry->irq_flags);
	}

	struct op_sample *op_cpu_buffer_read_entry(int cpu)
	{
	struct ring_buffer_event *e;
	e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
	if (e)
	return ring_buffer_event_data(e);
	if (ring_buffer_swap_cpu(op_ring_buffer_read,
	op_ring_buffer_write,
	cpu))
	return NULL;
	e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
	if (e)
	return ring_buffer_event_data(e);
	return NULL;
	}

	unsigned long op_cpu_buffer_entries(int cpu)
	{
	return ring_buffer_entries_cpu(op_ring_buffer_read, cpu)
	+ ring_buffer_entries_cpu(op_ring_buffer_write, cpu);
	}

	static inline int
	add_sample(struct oprofile_cpu_buffer *cpu_buf,
	unsigned long pc, unsigned long event)
	{
	struct op_entry entry;
	int ret;

	ret = op_cpu_buffer_write_entry(&entry);
	if (ret)
	return ret;

	entry.sample->eip = pc;
	entry.sample->event = event;

	ret = op_cpu_buffer_write_commit(&entry);
	if (ret)
	return ret;

	return 0;
	}

	static inline int
	add_code(struct oprofile_cpu_buffer *buffer, unsigned long value)
	{
	return add_sample(buffer, ESCAPE_CODE, value);
	}

	/* This must be safe from any context. It's safe writing here
	* because of the head/tail separation of the writer and reader
	* of the CPU buffer.
	*
	* is_kernel is needed because on some architectures you cannot
	* tell if you are in kernel or user space simply by looking at
	* pc. We tag this in the buffer by generating kernel enter/exit
	* events whenever is_kernel changes
	*/
	static int log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
	int is_kernel, unsigned long event)
	{
	struct task_struct *task;

	cpu_buf->sample_received++;

	if (pc == ESCAPE_CODE) {
	cpu_buf->sample_invalid_eip++;
	return 0;
	}

	is_kernel = !!is_kernel;

	task = current;

	/* notice a switch from user->kernel or vice versa */
	if (cpu_buf->last_is_kernel != is_kernel) {
	cpu_buf->last_is_kernel = is_kernel;
	if (add_code(cpu_buf, is_kernel))
	goto fail;
	}

	/* notice a task switch */
	if (cpu_buf->last_task != task) {
	cpu_buf->last_task = task;
	if (add_code(cpu_buf, (unsigned long)task))
	goto fail;
	}

	if (add_sample(cpu_buf, pc, event))
	goto fail;

	return 1;

	fail:
	cpu_buf->sample_lost_overflow++;
	return 0;
	}

	static int oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
	{
	add_code(cpu_buf, CPU_TRACE_BEGIN);
	cpu_buf->tracing = 1;
	return 1;
	}

	static void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
	{
	cpu_buf->tracing = 0;
	}

	static inline void
	__oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
	unsigned long event, int is_kernel)
	{
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);

	if (!oprofile_backtrace_depth) {
	log_sample(cpu_buf, pc, is_kernel, event);
	return;
	}

	if (!oprofile_begin_trace(cpu_buf))
	return;

	/*
	* if log_sample() fail we can't backtrace since we lost the
	* source of this event
	*/
	if (log_sample(cpu_buf, pc, is_kernel, event))
	oprofile_ops.backtrace(regs, oprofile_backtrace_depth);
	oprofile_end_trace(cpu_buf);
	}

	void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
	unsigned long event, int is_kernel)
	{
	__oprofile_add_ext_sample(pc, regs, event, is_kernel);
	}

	void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
	{
	int is_kernel = !user_mode(regs);
	unsigned long pc = profile_pc(regs);

	__oprofile_add_ext_sample(pc, regs, event, is_kernel);
	}

	#ifdef CONFIG_OPROFILE_IBS

	#define MAX_IBS_SAMPLE_SIZE 14

	void oprofile_add_ibs_sample(struct pt_regs * const regs,
	unsigned int * const ibs_sample, int ibs_code)
	{
	int is_kernel = !user_mode(regs);
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
	struct task_struct *task;
	int fail = 0;

	cpu_buf->sample_received++;

	/* notice a switch from user->kernel or vice versa */
	if (cpu_buf->last_is_kernel != is_kernel) {
	if (add_code(cpu_buf, is_kernel))
	goto fail;
	cpu_buf->last_is_kernel = is_kernel;
	}

	/* notice a task switch */
	if (!is_kernel) {
	task = current;
	if (cpu_buf->last_task != task) {
	if (add_code(cpu_buf, (unsigned long)task))
	goto fail;
	cpu_buf->last_task = task;
	}
	}

	fail = fail \|\| add_code(cpu_buf, ibs_code);
	fail = fail \|\| add_sample(cpu_buf, ibs_sample[0], ibs_sample[1]);
	fail = fail \|\| add_sample(cpu_buf, ibs_sample[2], ibs_sample[3]);
	fail = fail \|\| add_sample(cpu_buf, ibs_sample[4], ibs_sample[5]);

	if (ibs_code == IBS_OP_BEGIN) {
	fail = fail \|\| add_sample(cpu_buf, ibs_sample[6], ibs_sample[7]);
	fail = fail \|\| add_sample(cpu_buf, ibs_sample[8], ibs_sample[9]);
	fail = fail \|\| add_sample(cpu_buf, ibs_sample[10], ibs_sample[11]);
	}

	if (fail)
	goto fail;

	if (oprofile_backtrace_depth)
	oprofile_ops.backtrace(regs, oprofile_backtrace_depth);

	return;

	fail:
	cpu_buf->sample_lost_overflow++;
	return;
	}

	#endif

	void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
	{
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
	log_sample(cpu_buf, pc, is_kernel, event);
	}

	void oprofile_add_trace(unsigned long pc)
	{
	struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);

	if (!cpu_buf->tracing)
	return;

	/*
	* broken frame can give an eip with the same value as an
	* escape code, abort the trace if we get it
	*/
	if (pc == ESCAPE_CODE)
	goto fail;

	if (add_sample(cpu_buf, pc, 0))
	goto fail;

	return;
	fail:
	cpu_buf->tracing = 0;
	cpu_buf->backtrace_aborted++;
	return;
	}

	/*
	* This serves to avoid cpu buffer overflow, and makes sure
	* the task mortuary progresses
	*
	* By using schedule_delayed_work_on and then schedule_delayed_work
	* we guarantee this will stay on the correct cpu
	*/
	static void wq_sync_buffer(struct work_struct *work)
	{
	struct oprofile_cpu_buffer *b =
	container_of(work, struct oprofile_cpu_buffer, work.work);
	if (b->cpu != smp_processor_id()) {
	printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
	smp_processor_id(), b->cpu);

	if (!cpu_online(b->cpu)) {
	cancel_delayed_work(&b->work);
	return;
	}
	}
	sync_buffer(b->cpu);

	/* don't re-add the work if we're shutting down */
	if (work_enabled)
	schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
	}