samples/bpf/tracex3_kern.c

   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
  14 struct bpf_map_def SEC("maps") my_map = {
  15         .type = BPF_MAP_TYPE_HASH,
  16         .key_size = sizeof(long),
  17         .value_size = sizeof(u64),
  18         .max_entries = 4096,
  19 };
  20
  21 /* kprobe is NOT a stable ABI. If kernel internals change this bpf+kprobe
  22  * example will no longer be meaningful
  23  */
  24 SEC("kprobe/blk_mq_start_request")
  25 int 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
  34 static 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
  45 struct bpf_map_def SEC("maps") lat_map = {
  46         .type = BPF_MAP_TYPE_PERCPU_ARRAY,
  47         .key_size = sizeof(u32),
  48         .value_size = sizeof(u64),
  49         .max_entries = SLOTS,
  50 };
  51
  52 SEC("kprobe/blk_account_io_completion")
  53 int 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 }
  89 char _license[] SEC("license") = "GPL";
  90 u32 _version SEC("version") = LINUX_VERSION_CODE;