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samples/bpf/tracex3_kern.c
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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 <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/version.h>
#include <uapi/linux/bpf.h>
#include "bpf_helpers.h"
struct bpf_map_def SEC("maps") my_map = {
.type = BPF_MAP_TYPE_HASH,
.key_size = sizeof(long),
.value_size = sizeof(u64),
.max_entries = 4096,
};
/* 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 = ctx->di;
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 bpf_map_def SEC("maps") lat_map = {
.type = BPF_MAP_TYPE_ARRAY,
.key_size = sizeof(u32),
.value_size = sizeof(u64),
.max_entries = SLOTS,
};
SEC("kprobe/blk_update_request")
int bpf_prog2(struct pt_regs *ctx)
{
long rq = ctx->di;
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)
__sync_fetch_and_add((long *)value, 1);
return 0;
}
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;
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