linux/samples/bpf/tracex3_kern.c
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   1/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
   2 *
   3 * This program is free software; you can redistribute it and/or
   4 * modify it under the terms of version 2 of the GNU General Public
   5 * License as published by the Free Software Foundation.
   6 */
   7#include <linux/skbuff.h>
   8#include <linux/netdevice.h>
   9#include <linux/version.h>
  10#include <uapi/linux/bpf.h>
  11#include <bpf/bpf_helpers.h>
  12#include <bpf/bpf_tracing.h>
  13
  14struct {
  15        __uint(type, BPF_MAP_TYPE_HASH);
  16        __type(key, long);
  17        __type(value, u64);
  18        __uint(max_entries, 4096);
  19} my_map SEC(".maps");
  20
  21/* kprobe is NOT a stable ABI. If kernel internals change this bpf+kprobe
  22 * example will no longer be meaningful
  23 */
  24SEC("kprobe/blk_mq_start_request")
  25int bpf_prog1(struct pt_regs *ctx)
  26{
  27        long rq = PT_REGS_PARM1(ctx);
  28        u64 val = bpf_ktime_get_ns();
  29
  30        bpf_map_update_elem(&my_map, &rq, &val, BPF_ANY);
  31        return 0;
  32}
  33
  34static unsigned int log2l(unsigned long long n)
  35{
  36#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }
  37        int i = -(n == 0);
  38        S(32); S(16); S(8); S(4); S(2); S(1);
  39        return i;
  40#undef S
  41}
  42
  43#define SLOTS 100
  44
  45struct {
  46        __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
  47        __uint(key_size, sizeof(u32));
  48        __uint(value_size, sizeof(u64));
  49        __uint(max_entries, SLOTS);
  50} lat_map SEC(".maps");
  51
  52SEC("kprobe/blk_account_io_done")
  53int bpf_prog2(struct pt_regs *ctx)
  54{
  55        long rq = PT_REGS_PARM1(ctx);
  56        u64 *value, l, base;
  57        u32 index;
  58
  59        value = bpf_map_lookup_elem(&my_map, &rq);
  60        if (!value)
  61                return 0;
  62
  63        u64 cur_time = bpf_ktime_get_ns();
  64        u64 delta = cur_time - *value;
  65
  66        bpf_map_delete_elem(&my_map, &rq);
  67
  68        /* the lines below are computing index = log10(delta)*10
  69         * using integer arithmetic
  70         * index = 29 ~ 1 usec
  71         * index = 59 ~ 1 msec
  72         * index = 89 ~ 1 sec
  73         * index = 99 ~ 10sec or more
  74         * log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
  75         */
  76        l = log2l(delta);
  77        base = 1ll << l;
  78        index = (l * 64 + (delta - base) * 64 / base) * 3 / 64;
  79
  80        if (index >= SLOTS)
  81                index = SLOTS - 1;
  82
  83        value = bpf_map_lookup_elem(&lat_map, &index);
  84        if (value)
  85                *value += 1;
  86
  87        return 0;
  88}
  89char _license[] SEC("license") = "GPL";
  90u32 _version SEC("version") = LINUX_VERSION_CODE;
  91
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