#!/usr/bin/env bpftrace
/*
 * biostacks - Show disk I/O latency with initialization stacks.
 *
 * See BPF Performance Tools, Chapter 9, for an explanation of this tool.
 *
 * Copyright (c) 2019 Brendan Gregg.
 * Licensed under the Apache License, Version 2.0 (the "License").
 * This was originally created for the BPF Performance Tools book
 * published by Addison Wesley. ISBN-13: 9780136554820
 * When copying or porting, include this comment.
 *
 * 19-Mar-2019  Brendan Gregg   Created this.
 */

config = { missing_probes = "ignore" }

BEGIN
{
	printf("Tracing block I/O with init stacks. Hit Ctrl-C to end.\n");
}

kprobe:blk_account_io_start,
kprobe:__blk_account_io_start
{
	@reqstack[arg0] = kstack;
	@reqts[arg0] = nsecs;
}

kprobe:blk_start_request,
kprobe:blk_mq_start_request
/@reqts[arg0]/
{
	@usecs[@reqstack[arg0]] = hist(nsecs - @reqts[arg0]);
	delete(@reqstack[arg0]);
	delete(@reqts[arg0]);
}

END
{
	clear(@reqstack); clear(@reqts);
}