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/**
* @file cpu_buffer.c
*
* @remark Copyright 2002 OProfile authors
* @remark Read the file COPYING
*
* @author John Levon <levon@movementarian.org>
*
* 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/vmalloc.h>
#include <linux/errno.h>
#include "cpu_buffer.h"
#include "buffer_sync.h"
#include "oprof.h"
struct oprofile_cpu_buffer cpu_buffer[NR_CPUS] __cacheline_aligned;
static void wq_sync_buffer(void *);
#define DEFAULT_TIMER_EXPIRE (HZ / 10)
int work_enabled;
static void __free_cpu_buffers(int num)
{
int i;
for_each_online_cpu(i) {
if (cpu_buffer[i].buffer)
vfree(cpu_buffer[i].buffer);
}
}
int alloc_cpu_buffers(void)
{
int i;
unsigned long buffer_size = fs_cpu_buffer_size;
for_each_online_cpu(i) {
struct oprofile_cpu_buffer * b = &cpu_buffer[i];
b->buffer = vmalloc(sizeof(struct op_sample) * buffer_size);
if (!b->buffer)
goto fail;
b->last_task = NULL;
b->last_is_kernel = -1;
b->buffer_size = buffer_size;
b->tail_pos = 0;
b->head_pos = 0;
b->sample_received = 0;
b->sample_lost_overflow = 0;
b->cpu = i;
INIT_WORK(&b->work, wq_sync_buffer, b);
}
return 0;
fail:
__free_cpu_buffers(i);
return -ENOMEM;
}
void free_cpu_buffers(void)
{
__free_cpu_buffers(NR_CPUS);
}
void start_cpu_work(void)
{
int i;
work_enabled = 1;
for_each_online_cpu(i) {
struct oprofile_cpu_buffer * b = &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 = &cpu_buffer[i];
cancel_delayed_work(&b->work);
}
flush_scheduled_work();
}
/* compute number of available slots in cpu_buffer queue */
static unsigned long nr_available_slots(struct oprofile_cpu_buffer const * b)
{
unsigned long head = b->head_pos;
unsigned long tail = b->tail_pos;
if (tail > head)
return (tail - head) - 1;
return tail + (b->buffer_size - head) - 1;
}
static void increment_head(struct oprofile_cpu_buffer * b)
{
unsigned long new_head = b->head_pos + 1;
/* Ensure anything written to the slot before we
* increment is visible */
wmb();
if (new_head < (b->buffer_size))
b->head_pos = new_head;
else
b->head_pos = 0;
}
/* 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
* eip. We tag this in the buffer by generating kernel enter/exit
* events whenever is_kernel changes
*/
void oprofile_add_sample(unsigned long eip, unsigned int is_kernel,
unsigned long event, int cpu)
{
struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[cpu];
struct task_struct * task;
is_kernel = !!is_kernel;
cpu_buf->sample_received++;
if (nr_available_slots(cpu_buf) < 3) {
cpu_buf->sample_lost_overflow++;
return;
}
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;
cpu_buf->buffer[cpu_buf->head_pos].eip = ~0UL;
cpu_buf->buffer[cpu_buf->head_pos].event = is_kernel;
increment_head(cpu_buf);
}
/* notice a task switch */
if (cpu_buf->last_task != task) {
cpu_buf->last_task = task;
cpu_buf->buffer[cpu_buf->head_pos].eip = ~0UL;
cpu_buf->buffer[cpu_buf->head_pos].event = (unsigned long)task;
increment_head(cpu_buf);
}
cpu_buf->buffer[cpu_buf->head_pos].eip = eip;
cpu_buf->buffer[cpu_buf->head_pos].event = event;
increment_head(cpu_buf);
}
/* Resets the cpu buffer to a sane state. */
void cpu_buffer_reset(struct oprofile_cpu_buffer * cpu_buf)
{
/* reset these to invalid values; the next sample
* collected will populate the buffer with proper
* values to initialize the buffer
*/
cpu_buf->last_is_kernel = -1;
cpu_buf->last_task = NULL;
}
/*
* 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(void * data)
{
struct oprofile_cpu_buffer * b = (struct oprofile_cpu_buffer *)data;
if (b->cpu != smp_processor_id()) {
printk("WQ on CPU%d, prefer CPU%d\n",
smp_processor_id(), b->cpu);
}
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);
}
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