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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/samples/bpf/lathist_kern.c
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/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com

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 * Copyright (c) 2015 BMW Car IT GmbH

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 *

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 * This program is free software; you can redistribute it and/or

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 * modify it under the terms of version 2 of the GNU General Public

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 * License as published by the Free Software Foundation.

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 */

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#include <linux/version.h>

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#include <linux/ptrace.h>

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#include <uapi/linux/bpf.h>

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#include <bpf/bpf_helpers.h>

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#define MAX_ENTRIES	20

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#define MAX_CPU		4

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/* We need to stick to static allocated memory (an array instead of

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 * hash table) because managing dynamic memory from the

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 * trace_preempt_[on|off] tracepoints hooks is not supported.

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 */

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struct {

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	__uint(type, BPF_MAP_TYPE_ARRAY);

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	__type(key, int);

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	__type(value, u64);

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	__uint(max_entries, MAX_CPU);

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} my_map SEC(".maps");

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SEC("kprobe/trace_preempt_off")

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int bpf_prog1(struct pt_regs *ctx)

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{

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	int cpu = bpf_get_smp_processor_id();

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	u64 *ts = bpf_map_lookup_elem(&my_map, &cpu);

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	if (ts)

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		*ts = bpf_ktime_get_ns();

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	return 0;

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}

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static unsigned int log2(unsigned int v)

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{

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	unsigned int r;

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	unsigned int shift;

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	r = (v > 0xFFFF) << 4; v >>= r;

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	shift = (v > 0xFF) << 3; v >>= shift; r |= shift;

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	shift = (v > 0xF) << 2; v >>= shift; r |= shift;

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	shift = (v > 0x3) << 1; v >>= shift; r |= shift;

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	r |= (v >> 1);

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	return r;

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}

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static unsigned int log2l(unsigned long v)

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{

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	unsigned int hi = v >> 32;

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	if (hi)

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		return log2(hi) + 32;

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	else

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		return log2(v);

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}

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struct {

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	__uint(type, BPF_MAP_TYPE_ARRAY);

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	__type(key, int);

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	__type(value, long);

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	__uint(max_entries, MAX_CPU * MAX_ENTRIES);

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} my_lat SEC(".maps");

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SEC("kprobe/trace_preempt_on")

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int bpf_prog2(struct pt_regs *ctx)

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{

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	u64 *ts, cur_ts, delta;

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	int key, cpu;

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	long *val;

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	cpu = bpf_get_smp_processor_id();

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	ts = bpf_map_lookup_elem(&my_map, &cpu);

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	if (!ts)

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		return 0;

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	cur_ts = bpf_ktime_get_ns();

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	delta = log2l(cur_ts - *ts);

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	if (delta > MAX_ENTRIES - 1)

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		delta = MAX_ENTRIES - 1;

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	key = cpu * MAX_ENTRIES + delta;

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	val = bpf_map_lookup_elem(&my_lat, &key);

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	if (val)

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		__sync_fetch_and_add((long *)val, 1);

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	return 0;

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}

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char _license[] SEC("license") = "GPL";

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u32 _version SEC("version") = LINUX_VERSION_CODE;

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