text: /**
   * @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/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"
  
  struct oprofile_cpu_buffer cpu_buffer[NR_CPUS] __cacheline_aligned;
  
  static void wq_sync_buffer(void *);
  
  #define DEFAULT_TIMER_EXPIRE (HZ / 10)
  static int work_enabled;
  
  void free_cpu_buffers(void)
  {
  	int i;
   
  	for_each_online_cpu(i) {
  		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_node(sizeof(struct op_sample) * buffer_size,
  			cpu_to_node(i));
  		if (!b->buffer)
  			goto fail;
   
  		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->cpu = i;
  		INIT_WORK(&b->work, wq_sync_buffer, b);
  	}
  	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 = &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();
  }
  
  /* 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;
  }
  
  /* 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;
  }
  
  static inline void
  add_sample(struct oprofile_cpu_buffer * cpu_buf,
             unsigned long pc, unsigned long event)
  {
  	struct op_sample * entry = &cpu_buf->buffer[cpu_buf->head_pos];
  	entry->eip = pc;
  	entry->event = event;
  	increment_head(cpu_buf);
  }
  
  static inline void
  add_code(struct oprofile_cpu_buffer * buffer, unsigned long value)
  {
  	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 (nr_available_slots(cpu_buf) < 3) {
  		cpu_buf->sample_lost_overflow++;
  		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;
  		add_code(cpu_buf, is_kernel);
  	}
  
  	/* notice a task switch */
  	if (cpu_buf->last_task != task) {
  		cpu_buf->last_task = task;
  		add_code(cpu_buf, (unsigned long)task);
  	}
   
  	add_sample(cpu_buf, pc, event);
  	return 1;
  }
  
  static int oprofile_begin_trace(struct oprofile_cpu_buffer * cpu_buf)
  {
  	if (nr_available_slots(cpu_buf) < 4) {
  		cpu_buf->sample_lost_overflow++;
  		return 0;
  	}
  
  	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;
  }
  
  void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
  {
  	struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
  	unsigned long pc = profile_pc(regs);
  	int is_kernel = !user_mode(regs);
  
  	if (!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, backtrace_depth);
  	oprofile_end_trace(cpu_buf);
  }
  
  void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
  {
  	struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
  	log_sample(cpu_buf, pc, is_kernel, event);
  }
  
  void oprofile_add_trace(unsigned long pc)
  {
  	struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
  
  	if (!cpu_buf->tracing)
  		return;
  
  	if (nr_available_slots(cpu_buf) < 1) {
  		cpu_buf->tracing = 0;
  		cpu_buf->sample_lost_overflow++;
  		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) {
  		cpu_buf->tracing = 0;
  		cpu_buf->backtrace_aborted++;
  		return;
  	}
  
  	add_sample(cpu_buf, pc, 0);
  }
  
  /*
   * 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 = 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);
  }
  