examples/vfsreadlat.c

/*
 * vfsreadlat.c		VFS read latency distribution.
 *			For Linux, uses BCC, eBPF. See .py file.
 *
 * Based on eBPF sample tracex2 by Alexi Starovoitov.
 * 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.
 *
 * 15-Aug-2015	Brendan Gregg	Created this.
 */

#include <uapi/linux/ptrace.h>

BPF_HASH(start, u32);
BPF_TABLE("array", int, u64, dist, 64);

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 + 1;
	else
		return log2(v) + 1;
}

int do_entry(struct pt_regs *ctx)
{
	u32 pid;
	u64 ts, *val;

	pid = bpf_get_current_pid_tgid();
	ts = bpf_ktime_get_ns();
	start.update(&pid, &ts);
	return 0;
}

int do_return(struct pt_regs *ctx)
{
	u32 pid;
	u64 *tsp, delta;

	pid = bpf_get_current_pid_tgid();
	tsp = start.lookup(&pid);

	if (tsp != 0) {
		delta = bpf_ktime_get_ns() - *tsp;
		int index = log2l(delta / 1000);
		u64 *leaf = dist.lookup(&index);
		if (leaf) (*leaf)++;
		start.delete(&pid);
	}

	return 0;
}