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 {
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 */
24 SEC("kprobe/blk_mq_start_request")
bpf_prog1(struct pt_regs * ctx)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
log2l(unsigned long long n)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 {
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
52 SEC("kprobe/blk_account_io_done")
bpf_prog2(struct pt_regs * ctx)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;
91