LXR linux/samples/bpf/lathist

   1/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
   2 * Copyright (c) 2015 BMW Car IT GmbH
   3 *
   4 * This program is free software; you can redistribute it and/or
   5 * modify it under the terms of version 2 of the GNU General Public
   6 * License as published by the Free Software Foundation.
   7 */
   8#include <linux/version.h>
   9#include <linux/ptrace.h>
  10#include <uapi/linux/bpf.h>
  11#include "bpf_helpers.h"
  12
  13#define MAX_ENTRIES     20
  14#define MAX_CPU         4
  15
  16/* We need to stick to static allocated memory (an array instead of
  17 * hash table) because managing dynamic memory from the
  18 * trace_preempt_[on|off] tracepoints hooks is not supported.
  19 */
  20
  21struct bpf_map_def SEC("maps") my_map = {
  22        .type = BPF_MAP_TYPE_ARRAY,
  23        .key_size = sizeof(int),
  24        .value_size = sizeof(u64),
  25        .max_entries = MAX_CPU,
  26};
  27
  28SEC("kprobe/trace_preempt_off")
  29int bpf_prog1(struct pt_regs *ctx)
  30{
  31        int cpu = bpf_get_smp_processor_id();
  32        u64 *ts = bpf_map_lookup_elem(&my_map, &cpu);
  33
  34        if (ts)
  35                *ts = bpf_ktime_get_ns();
  36
  37        return 0;
  38}
  39
  40static unsigned int log2(unsigned int v)
  41{
  42        unsigned int r;
  43        unsigned int shift;
  44
  45        r = (v > 0xFFFF) << 4; v >>= r;
  46        shift = (v > 0xFF) << 3; v >>= shift; r |= shift;
  47        shift = (v > 0xF) << 2; v >>= shift; r |= shift;
  48        shift = (v > 0x3) << 1; v >>= shift; r |= shift;
  49        r |= (v >> 1);
  50
  51        return r;
  52}
  53
  54static unsigned int log2l(unsigned long v)
  55{
  56        unsigned int hi = v >> 32;
  57
  58        if (hi)
  59                return log2(hi) + 32;
  60        else
  61                return log2(v);
  62}
  63
  64struct bpf_map_def SEC("maps") my_lat = {
  65        .type = BPF_MAP_TYPE_ARRAY,
  66        .key_size = sizeof(int),
  67        .value_size = sizeof(long),
  68        .max_entries = MAX_CPU * MAX_ENTRIES,
  69};
  70
  71SEC("kprobe/trace_preempt_on")
  72int bpf_prog2(struct pt_regs *ctx)
  73{
  74        u64 *ts, cur_ts, delta;
  75        int key, cpu;
  76        long *val;
  77
  78        cpu = bpf_get_smp_processor_id();
  79        ts = bpf_map_lookup_elem(&my_map, &cpu);
  80        if (!ts)
  81                return 0;
  82
  83        cur_ts = bpf_ktime_get_ns();
  84        delta = log2l(cur_ts - *ts);
  85
  86        if (delta > MAX_ENTRIES - 1)
  87                delta = MAX_ENTRIES - 1;
  88
  89        key = cpu * MAX_ENTRIES + delta;
  90        val = bpf_map_lookup_elem(&my_lat, &key);
  91        if (val)
  92                __sync_fetch_and_add((long *)val, 1);
  93
  94        return 0;
  95
  96}
  97
  98char _license[] SEC("license") = "GPL";
  99u32 _version SEC("version") = LINUX_VERSION_CODE;
 100