/*
   * latencytop.c: Latency display infrastructure
   *
   * (C) Copyright 2008 Intel Corporation
   * Author: Arjan van de Ven <arjan@linux.intel.com>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; version 2
   * of the License.
   */

  
  /*
   * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is
   * used by the "latencytop" userspace tool. The latency that is tracked is not
   * the 'traditional' interrupt latency (which is primarily caused by something
   * else consuming CPU), but instead, it is the latency an application encounters
   * because the kernel sleeps on its behalf for various reasons.
   *
   * This code tracks 2 levels of statistics:
   * 1) System level latency
   * 2) Per process latency
   *
   * The latency is stored in fixed sized data structures in an accumulated form;
   * if the "same" latency cause is hit twice, this will be tracked as one entry
   * in the data structure. Both the count, total accumulated latency and maximum
   * latency are tracked in this data structure. When the fixed size structure is
   * full, no new causes are tracked until the buffer is flushed by writing to
   * the /proc file; the userspace tool does this on a regular basis.
   *
   * A latency cause is identified by a stringified backtrace at the point that
   * the scheduler gets invoked. The userland tool will use this string to
   * identify the cause of the latency in human readable form.
   *
   * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
   * These files look like this:
   *
   * Latency Top version : v0.1
   * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
   * |    |    |    |
   * |    |    |    +----> the stringified backtrace
   * |    |    +---------> The maximum latency for this entry in microseconds
   * |    +--------------> The accumulated latency for this entry (microseconds)
   * +-------------------> The number of times this entry is hit
   *
   * (note: the average latency is the accumulated latency divided by the number
   * of times)
   */

  #include <linux/latencytop.h>
  #include <linux/kallsyms.h>
  #include <linux/seq_file.h>
  #include <linux/notifier.h>
  #include <linux/spinlock.h>
  #include <linux/proc_fs.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/list.h>

  #include <linux/stacktrace.h>
  
  static DEFINE_SPINLOCK(latency_lock);
  
  #define MAXLR 128
  static struct latency_record latency_record[MAXLR];
  
  int latencytop_enabled;
  
  void clear_all_latency_tracing(struct task_struct *p)
  {
  	unsigned long flags;
  
  	if (!latencytop_enabled)
  		return;
  
  	spin_lock_irqsave(&latency_lock, flags);
  	memset(&p->latency_record, 0, sizeof(p->latency_record));
  	p->latency_record_count = 0;
  	spin_unlock_irqrestore(&latency_lock, flags);
  }
  
  static void clear_global_latency_tracing(void)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&latency_lock, flags);
  	memset(&latency_record, 0, sizeof(latency_record));
  	spin_unlock_irqrestore(&latency_lock, flags);
  }
  
  static void __sched
  account_global_scheduler_latency(struct task_struct *tsk, struct latency_record *lat)
  {
  	int firstnonnull = MAXLR + 1;
  	int i;
  
  	if (!latencytop_enabled)
  		return;
  
  	/* skip kernel threads for now */
  	if (!tsk->mm)
  		return;
  
  	for (i = 0; i < MAXLR; i++) {

  		int q, same = 1;

  		/* Nothing stored: */
  		if (!latency_record[i].backtrace[0]) {
  			if (firstnonnull > i)
  				firstnonnull = i;
  			continue;
  		}

  		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {

  			unsigned long record = lat->backtrace[q];
  
  			if (latency_record[i].backtrace[q] != record) {

  				same = 0;

  				break;

  			}
  
  			/* 0 and ULONG_MAX entries mean end of backtrace: */
  			if (record == 0 || record == ULONG_MAX)

  				break;
  		}
  		if (same) {
  			latency_record[i].count++;
  			latency_record[i].time += lat->time;
  			if (lat->time > latency_record[i].max)
  				latency_record[i].max = lat->time;
  			return;
  		}
  	}
  
  	i = firstnonnull;
  	if (i >= MAXLR - 1)
  		return;
  
  	/* Allocted a new one: */
  	memcpy(&latency_record[i], lat, sizeof(struct latency_record));
  }

  /*
   * Iterator to store a backtrace into a latency record entry
   */
  static inline void store_stacktrace(struct task_struct *tsk,
  					struct latency_record *lat)

  {
  	struct stack_trace trace;
  
  	memset(&trace, 0, sizeof(trace));
  	trace.max_entries = LT_BACKTRACEDEPTH;
  	trace.entries = &lat->backtrace[0];

  	save_stack_trace_tsk(tsk, &trace);
  }

  /**

   * __account_scheduler_latency - record an occurred latency

   * @tsk - the task struct of the task hitting the latency
   * @usecs - the duration of the latency in microseconds
   * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
   *
   * This function is the main entry point for recording latency entries
   * as called by the scheduler.
   *
   * This function has a few special cases to deal with normal 'non-latency'
   * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
   * since this usually is caused by waiting for events via select() and co.
   *
   * Negative latencies (caused by time going backwards) are also explicitly
   * skipped.
   */

  void __sched

  __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)

  {
  	unsigned long flags;
  	int i, q;
  	struct latency_record lat;

  	/* Long interruptible waits are generally user requested... */
  	if (inter && usecs > 5000)
  		return;

  	/* Negative sleeps are time going backwards */
  	/* Zero-time sleeps are non-interesting */
  	if (usecs <= 0)
  		return;

  	memset(&lat, 0, sizeof(lat));
  	lat.count = 1;
  	lat.time = usecs;
  	lat.max = usecs;
  	store_stacktrace(tsk, &lat);
  
  	spin_lock_irqsave(&latency_lock, flags);
  
  	account_global_scheduler_latency(tsk, &lat);

  	for (i = 0; i < tsk->latency_record_count; i++) {

  		struct latency_record *mylat;
  		int same = 1;

  		mylat = &tsk->latency_record[i];

  		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {

  			unsigned long record = lat.backtrace[q];
  
  			if (mylat->backtrace[q] != record) {

  				same = 0;

  				break;

  			}
  
  			/* 0 and ULONG_MAX entries mean end of backtrace: */
  			if (record == 0 || record == ULONG_MAX)

  				break;
  		}
  		if (same) {
  			mylat->count++;
  			mylat->time += lat.time;
  			if (lat.time > mylat->max)
  				mylat->max = lat.time;
  			goto out_unlock;
  		}
  	}

  	/*
  	 * short term hack; if we're > 32 we stop; future we recycle:
  	 */
  	if (tsk->latency_record_count >= LT_SAVECOUNT)
  		goto out_unlock;

  	/* Allocated a new one: */

  	i = tsk->latency_record_count++;

  	memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
  
  out_unlock:
  	spin_unlock_irqrestore(&latency_lock, flags);
  }
  
  static int lstats_show(struct seq_file *m, void *v)
  {
  	int i;
  
  	seq_puts(m, "Latency Top version : v0.1
  ");
  
  	for (i = 0; i < MAXLR; i++) {

  		struct latency_record *lr = &latency_record[i];
  
  		if (lr->backtrace[0]) {

  			int q;

  			seq_printf(m, "%i %lu %lu",
  				   lr->count, lr->time, lr->max);

  			for (q = 0; q < LT_BACKTRACEDEPTH; q++) {

  				unsigned long bt = lr->backtrace[q];
  				if (!bt)

  					break;

  				if (bt == ULONG_MAX)

  					break;

  				seq_printf(m, " %ps", (void *)bt);

  			}
  			seq_printf(m, "
  ");
  		}
  	}
  	return 0;
  }
  
  static ssize_t
  lstats_write(struct file *file, const char __user *buf, size_t count,
  	     loff_t *offs)
  {
  	clear_global_latency_tracing();
  
  	return count;
  }
  
  static int lstats_open(struct inode *inode, struct file *filp)
  {
  	return single_open(filp, lstats_show, NULL);
  }

  static const struct file_operations lstats_fops = {

  	.open		= lstats_open,
  	.read		= seq_read,
  	.write		= lstats_write,
  	.llseek		= seq_lseek,
  	.release	= single_release,
  };
  
  static int __init init_lstats_procfs(void)
  {

  	proc_create("latency_stats", 0644, NULL, &lstats_fops);

  	return 0;
  }

  device_initcall(init_lstats_procfs);