linux-imx

// SPDX-License-Identifier: GPL-2.0-only

/*

 * latencytop.c: Latency display infrastructure

 *

 * (C) Copyright 2008 Intel Corporation

 * Author: Arjan van de Ven <arjan@linux.intel.com>

 */

​

/*

 * 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/kallsyms.h>

#include <linux/seq_file.h>

#include <linux/notifier.h>

#include <linux/spinlock.h>

#include <linux/proc_fs.h>

#include <linux/latencytop.h>

#include <linux/export.h>

#include <linux/sched.h>

#include <linux/sched/debug.h>

#include <linux/sched/stat.h>

#include <linux/list.h>

#include <linux/stacktrace.h>

​

static DEFINE_RAW_SPINLOCK(latency_lock);

​

#define MAXLR 128

static struct latency_record latency_record[MAXLR];

​