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 "vmlinux.h"
  8#include <linux/version.h>
  9#include <bpf/bpf_helpers.h>
 10#include <bpf/bpf_tracing.h>
 11
 12struct start_key {
 13	dev_t dev;
 14	u32 _pad;
 15	sector_t sector;
 16};
 17
 18struct {
 19	__uint(type, BPF_MAP_TYPE_HASH);
 20	__type(key, long);
 21	__type(value, u64);
 22	__uint(max_entries, 4096);
 23} my_map SEC(".maps");
 24
 25/* from /sys/kernel/tracing/events/block/block_io_start/format */
 26SEC("tracepoint/block/block_io_start")
 27int bpf_prog1(struct trace_event_raw_block_rq *ctx)
 28{
 29	u64 val = bpf_ktime_get_ns();
 30	struct start_key key = {
 31		.dev = ctx->dev,
 32		.sector = ctx->sector
 33	};
 34
 35	bpf_map_update_elem(&my_map, &key, &val, BPF_ANY);
 36	return 0;
 37}
 38
 39static unsigned int log2l(unsigned long long n)
 40{
 41#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }
 42	int i = -(n == 0);
 43	S(32); S(16); S(8); S(4); S(2); S(1);
 44	return i;
 45#undef S
 46}
 47
 48#define SLOTS 100
 49
 50struct {
 51	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
 52	__uint(key_size, sizeof(u32));
 53	__uint(value_size, sizeof(u64));
 54	__uint(max_entries, SLOTS);
 55} lat_map SEC(".maps");
 56
 57/* from /sys/kernel/tracing/events/block/block_io_done/format */
 58SEC("tracepoint/block/block_io_done")
 59int bpf_prog2(struct trace_event_raw_block_rq *ctx)
 60{
 61	struct start_key key = {
 62		.dev = ctx->dev,
 63		.sector = ctx->sector
 64	};
 65
 66	u64 *value, l, base;
 67	u32 index;
 68
 69	value = bpf_map_lookup_elem(&my_map, &key);
 70	if (!value)
 71		return 0;
 72
 73	u64 cur_time = bpf_ktime_get_ns();
 74	u64 delta = cur_time - *value;
 75
 76	bpf_map_delete_elem(&my_map, &key);
 77
 78	/* the lines below are computing index = log10(delta)*10
 79	 * using integer arithmetic
 80	 * index = 29 ~ 1 usec
 81	 * index = 59 ~ 1 msec
 82	 * index = 89 ~ 1 sec
 83	 * index = 99 ~ 10sec or more
 84	 * log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
 85	 */
 86	l = log2l(delta);
 87	base = 1ll << l;
 88	index = (l * 64 + (delta - base) * 64 / base) * 3 / 64;
 89
 90	if (index >= SLOTS)
 91		index = SLOTS - 1;
 92
 93	value = bpf_map_lookup_elem(&lat_map, &index);
 94	if (value)
 95		*value += 1;
 96
 97	return 0;
 98}
 99char _license[] SEC("license") = "GPL";
100u32 _version SEC("version") = LINUX_VERSION_CODE;