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;