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/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*/
#include "vmlinux.h"
#include <linux/version.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__type(key, long);
__type(value, u64);
__uint(max_entries, 4096);
} my_map SEC(".maps");
/* kprobe is NOT a stable ABI. If kernel internals change this bpf+kprobe
* example will no longer be meaningful
*/
SEC("kprobe/blk_mq_start_request")
int bpf_prog1(struct pt_regs *ctx)
{
long rq = PT_REGS_PARM1(ctx);
u64 val = bpf_ktime_get_ns();
bpf_map_update_elem(&my_map, &rq, &val, BPF_ANY);
return 0;
}
static unsigned int log2l(unsigned long long n)
{
#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }
int i = -(n == 0);
S(32); S(16); S(8); S(4); S(2); S(1);
return i;
#undef S
}
#define SLOTS 100
struct {
__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
__uint(key_size, sizeof(u32));
__uint(value_size, sizeof(u64));
__uint(max_entries, SLOTS);
} lat_map SEC(".maps");
SEC("kprobe/__blk_account_io_done")
int bpf_prog2(struct pt_regs *ctx)
{
long rq = PT_REGS_PARM1(ctx);
u64 *value, l, base;
u32 index;
value = bpf_map_lookup_elem(&my_map, &rq);
if (!value)
return 0;
u64 cur_time = bpf_ktime_get_ns();
u64 delta = cur_time - *value;
bpf_map_delete_elem(&my_map, &rq);
/* the lines below are computing index = log10(delta)*10
* using integer arithmetic
* index = 29 ~ 1 usec
* index = 59 ~ 1 msec
* index = 89 ~ 1 sec
* index = 99 ~ 10sec or more
* log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
*/
l = log2l(delta);
base = 1ll << l;
index = (l * 64 + (delta - base) * 64 / base) * 3 / 64;
if (index >= SLOTS)
index = SLOTS - 1;
value = bpf_map_lookup_elem(&lat_map, &index);
if (value)
*value += 1;
return 0;
}
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;
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