lathist_kern.c
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/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
* Copyright (c) 2015 BMW Car IT GmbH
*
* 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/version.h>
#include <linux/ptrace.h>
#include <uapi/linux/bpf.h>
#include "bpf_helpers.h"
#define MAX_ENTRIES 20
#define MAX_CPU 4
/* We need to stick to static allocated memory (an array instead of
* hash table) because managing dynamic memory from the
* trace_preempt_[on|off] tracepoints hooks is not supported.
*/
struct bpf_map_def SEC("maps") my_map = {
.type = BPF_MAP_TYPE_ARRAY,
.key_size = sizeof(int),
.value_size = sizeof(u64),
.max_entries = MAX_CPU,
};
SEC("kprobe/trace_preempt_off")
int bpf_prog1(struct pt_regs *ctx)
{
int cpu = bpf_get_smp_processor_id();
u64 *ts = bpf_map_lookup_elem(&my_map, &cpu);
if (ts)
*ts = bpf_ktime_get_ns();
return 0;
}
static unsigned int log2(unsigned int v)
{
unsigned int r;
unsigned int shift;
r = (v > 0xFFFF) << 4; v >>= r;
shift = (v > 0xFF) << 3; v >>= shift; r |= shift;
shift = (v > 0xF) << 2; v >>= shift; r |= shift;
shift = (v > 0x3) << 1; v >>= shift; r |= shift;
r |= (v >> 1);
return r;
}
static unsigned int log2l(unsigned long v)
{
unsigned int hi = v >> 32;
if (hi)
return log2(hi) + 32;
else
return log2(v);
}
struct bpf_map_def SEC("maps") my_lat = {
.type = BPF_MAP_TYPE_ARRAY,
.key_size = sizeof(int),
.value_size = sizeof(long),
.max_entries = MAX_CPU * MAX_ENTRIES,
};
SEC("kprobe/trace_preempt_on")
int bpf_prog2(struct pt_regs *ctx)
{
u64 *ts, cur_ts, delta;
int key, cpu;
long *val;
cpu = bpf_get_smp_processor_id();
ts = bpf_map_lookup_elem(&my_map, &cpu);
if (!ts)
return 0;
cur_ts = bpf_ktime_get_ns();
delta = log2l(cur_ts - *ts);
if (delta > MAX_ENTRIES - 1)
delta = MAX_ENTRIES - 1;
key = cpu * MAX_ENTRIES + delta;
val = bpf_map_lookup_elem(&my_lat, &key);
if (val)
__sync_fetch_and_add((long *)val, 1);
return 0;
}
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;