samples/bpf/lathist_kern.c

0001 /* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
0002  * Copyright (c) 2015 BMW Car IT GmbH
0003  *
0004  * This program is free software; you can redistribute it and/or
0005  * modify it under the terms of version 2 of the GNU General Public
0006  * License as published by the Free Software Foundation.
0007  */
0008 #include <linux/version.h>
0009 #include <linux/ptrace.h>
0010 #include <uapi/linux/bpf.h>
0011 #include <bpf/bpf_helpers.h>
0012
0013 #define MAX_ENTRIES 20
0014 #define MAX_CPU     4
0015
0016 /* We need to stick to static allocated memory (an array instead of
0017  * hash table) because managing dynamic memory from the
0018  * trace_preempt_[on|off] tracepoints hooks is not supported.
0019  */
0020
0021 struct {
0022     __uint(type, BPF_MAP_TYPE_ARRAY);
0023     __type(key, int);
0024     __type(value, u64);
0025     __uint(max_entries, MAX_CPU);
0026 } my_map SEC(".maps");
0027
0028 SEC("kprobe/trace_preempt_off")
0029 int bpf_prog1(struct pt_regs *ctx)
0030 {
0031     int cpu = bpf_get_smp_processor_id();
0032     u64 *ts = bpf_map_lookup_elem(&my_map, &cpu);
0033
0034     if (ts)
0035         *ts = bpf_ktime_get_ns();
0036
0037     return 0;
0038 }
0039
0040 static unsigned int log2(unsigned int v)
0041 {
0042     unsigned int r;
0043     unsigned int shift;
0044
0045     r = (v > 0xFFFF) << 4; v >>= r;
0046     shift = (v > 0xFF) << 3; v >>= shift; r |= shift;
0047     shift = (v > 0xF) << 2; v >>= shift; r |= shift;
0048     shift = (v > 0x3) << 1; v >>= shift; r |= shift;
0049     r |= (v >> 1);
0050
0051     return r;
0052 }
0053
0054 static unsigned int log2l(unsigned long v)
0055 {
0056     unsigned int hi = v >> 32;
0057
0058     if (hi)
0059         return log2(hi) + 32;
0060     else
0061         return log2(v);
0062 }
0063
0064 struct {
0065     __uint(type, BPF_MAP_TYPE_ARRAY);
0066     __type(key, int);
0067     __type(value, long);
0068     __uint(max_entries, MAX_CPU * MAX_ENTRIES);
0069 } my_lat SEC(".maps");
0070
0071 SEC("kprobe/trace_preempt_on")
0072 int bpf_prog2(struct pt_regs *ctx)
0073 {
0074     u64 *ts, cur_ts, delta;
0075     int key, cpu;
0076     long *val;
0077
0078     cpu = bpf_get_smp_processor_id();
0079     ts = bpf_map_lookup_elem(&my_map, &cpu);
0080     if (!ts)
0081         return 0;
0082
0083     cur_ts = bpf_ktime_get_ns();
0084     delta = log2l(cur_ts - *ts);
0085
0086     if (delta > MAX_ENTRIES - 1)
0087         delta = MAX_ENTRIES - 1;
0088
0089     key = cpu * MAX_ENTRIES + delta;
0090     val = bpf_map_lookup_elem(&my_lat, &key);
0091     if (val)
0092         __sync_fetch_and_add((long *)val, 1);
0093
0094     return 0;
0095
0096 }
0097
0098 char _license[] SEC("license") = "GPL";
0099 u32 _version SEC("version") = LINUX_VERSION_CODE;