/**
 * @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, 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;
}

#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(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(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();
}

/*
 * 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);
        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);
        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, backtrace, is_kernel, current))
                goto fail;

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

        return 1;

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

static inline void oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
{
        cpu_buf->tracing = 1;
}

static inline 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);
        unsigned long backtrace = oprofile_backtrace_depth;

        /*
         * if log_sample() fail we can't backtrace since we lost the
         * source of this event
         */
        if (!log_sample(cpu_buf, pc, backtrace, is_kernel, event))
                /* failed */
                return;

        if (!backtrace)
                return;

        oprofile_begin_trace(cpu_buf);
        oprofile_ops.backtrace(regs, backtrace);
        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);
}

/*
 * Add samples with data to the ring buffer.
 *
 * Use oprofile_add_data(&entry, val) to add data and
 * oprofile_write_commit(&entry) to commit the sample.
 */
void
oprofile_write_reserve(struct op_entry *entry, struct pt_regs * const regs,
                       unsigned long pc, int code, int size)
{
        struct op_sample *sample;
        int is_kernel = !user_mode(regs);
        struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);

        cpu_buf->sample_received++;

        /* no backtraces for samples with data */
        if (op_add_code(cpu_buf, 0, is_kernel, current))
                goto fail;

        sample = op_cpu_buffer_write_reserve(entry, size + 2);
        if (!sample)
                goto fail;
        sample->eip = ESCAPE_CODE;
        sample->event = 0;              /* no flags */

        op_cpu_buffer_add_data(entry, code);
        op_cpu_buffer_add_data(entry, pc);

        return;

fail:
        entry->event = NULL;
        cpu_buf->sample_lost_overflow++;
}

int oprofile_add_data(struct op_entry *entry, unsigned long val)
{
        if (!entry->event)
                return 0;
        return op_cpu_buffer_add_data(entry, val);
}

int oprofile_add_data64(struct op_entry *entry, u64 val)
{
        if (!entry->event)
                return 0;
        if (op_cpu_buffer_get_size(entry) < 2)
                /*
                 * the function returns 0 to indicate a too small
                 * buffer, even if there is some space left
                 */
                return 0;
        if (!op_cpu_buffer_add_data(entry, (u32)val))
                return 0;
        return op_cpu_buffer_add_data(entry, (u32)(val >> 32));
}

int oprofile_write_commit(struct op_entry *entry)
{
        if (!entry->event)
                return -EINVAL;
        return op_cpu_buffer_write_commit(entry);
}

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, 0, 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 (op_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);
}