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|
/**
* @file cpu_buffer.c
*
* @remark Copyright 2002-2009 OProfile authors
* @remark Read the file COPYING
*
* @author John Levon <levon@movementarian.org>
* @author Barry Kasindorf <barry.kasindorf@amd.com>
* @author Robert Richter <robert.richter@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/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, op_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(op_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;
}
#define RB_EVENT_HDR_SIZE 4
int alloc_cpu_buffers(void)
{
int i;
unsigned long buffer_size = oprofile_cpu_buffer_size;
unsigned long byte_size = buffer_size * (sizeof(struct op_sample) +
RB_EVENT_HDR_SIZE);
op_ring_buffer_read = ring_buffer_alloc(byte_size, OP_BUFFER_FLAGS);
if (!op_ring_buffer_read)
goto fail;
op_ring_buffer_write = ring_buffer_alloc(byte_size, OP_BUFFER_FLAGS);
if (!op_ring_buffer_write)
goto fail;
for_each_possible_cpu(i) {
struct oprofile_cpu_buffer *b = &per_cpu(op_cpu_buffer, i);
b->last_task = NULL;
b->last_is_kernel = -1;
b->tracing = 0;
b->buffer_size = buffer_size;
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(op_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(op_cpu_buffer, i);
cancel_delayed_work(&b->work);
}
flush_scheduled_work();
}
/*
* This function prepares the cpu buffer to write a sample.
*
* Struct op_entry is used during operations on the ring buffer while
* struct op_sample contains the data that is stored in the ring
* buffer. Struct entry can be uninitialized. The function reserves a
* data array that is specified by size. Use
* op_cpu_buffer_write_commit() after preparing the sample. In case of
* errors a null pointer is returned, otherwise the pointer to the
* sample.
*
*/
struct op_sample
*op_cpu_buffer_write_reserve(struct op_entry *entry, unsigned long size)
{
entry->event = ring_buffer_lock_reserve
(op_ring_buffer_write, sizeof(struct op_sample) +
size * sizeof(entry->sample->data[0]));
if (entry->event)
entry->sample = ring_buffer_event_data(entry->event);
else
entry->sample = NULL;
if (!entry->sample)
return NULL;
entry->size = size;
entry->data = entry->sample->data;
return entry->sample;
}
int op_cpu_buffer_write_commit(struct op_entry *entry)
{
return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event);
}
struct op_sample *op_cpu_buffer_read_entry(struct op_entry *entry, int cpu)
{
struct ring_buffer_event *e;
e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL, NULL);
if (e)
goto event;
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, NULL);
if (e)
goto event;
return NULL;
event:
entry->event = e;
entry->sample = ring_buffer_event_data(e);
entry->size = (ring_buffer_event_length(e) - sizeof(struct op_sample))
/ sizeof(entry->sample->data[0]);
entry->data = entry->sample->data;
return entry->sample;
}
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 int
op_add_code(struct oprofile_cpu_buffer *cpu_buf, unsigned long backtrace,
int is_kernel, struct task_struct *task)
{
struct op_entry entry;
struct op_sample *sample;
unsigned long flags;
int size;
flags = 0;
if (backtrace)
flags |= TRACE_BEGIN;
/* notice a switch from user->kernel or vice versa */
is_kernel = !!is_kernel;
if (cpu_buf->last_is_kernel != is_kernel) {
cpu_buf->last_is_kernel = is_kernel;
flags |= KERNEL_CTX_SWITCH;
if (is_kernel)
flags |= IS_KERNEL;
}
/* notice a task switch */
if (cpu_buf->last_task != task) {
cpu_buf->last_task = task;
flags |= USER_CTX_SWITCH;
}
if (!flags)
/* nothing to do */
return 0;
if (flags & USER_CTX_SWITCH)
size = 1;
else
size = 0;
sample = op_cpu_buffer_write_reserve(&entry, size);
if (!sample)
return -ENOMEM;
sample->eip = ESCAPE_CODE;
sample->event = flags;
if (size)
op_cpu_buffer_add_data(&entry, (unsigned long)task);
op_cpu_buffer_write_commit(&entry);
return 0;
}
static inline int
op_add_sample(struct oprofile_cpu_buffer *cpu_buf,
unsigned long pc, unsigned long event)
{
struct op_entry entry;
struct op_sample *sample;
sample = op_cpu_buffer_write_reserve(&entry, 0);
if (!sample)
return -ENOMEM;
sample->eip = pc;
sample->event = event;
return op_cpu_buffer_write_commit(&entry);
}
/*
* This must be safe from any context.
*
* 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,
unsigned long backtrace, int is_kernel, unsigned long event)
{
cpu_buf->sample_received++;
if (pc == ESCAPE_CODE) {
cpu_buf->sample_invalid_eip++;
return 0;
}
if (op_add_code(cpu_buf,
|