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Filename : bitesize-nd.stp
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#!/usr/bin/stap
/*
 * bitesize-nd.stp	Measure storage (bio) I/O size distribution.
 *			For Linux, uses SystemTap (non-debuginfo).
 *
 * USAGE: ./bitesize-nd.stp
 *
 * This script uses the kernel tracepoint block_rq_insert. The output includes
 * the name of the process or thread that was on-CPU when the I/O request was
 * inserted on the issue queue.
 *
 * From systemtap-lwtools: https://github.com/brendangregg/systemtap-lwtools
 *
 * See the corresponding man page (in systemtap-lwtools) for more info.
 *
 * Copyright (C) 2015 Brendan Gregg.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * 01-Feb-2015	Brendan Gregg	Created this.
 */

global sz;

probe begin
{
	printf("Tracing block I/O... Hit Ctrl-C to end.\n");
}

probe kernel.trace("block_rq_insert") {
	/*
	 * You aren't supposed to access __data_len directly as it is internal,
	 * but I don't see another way...
	 */
	sz[execname()] <<< $rq->__data_len;
}

probe end
{
	printf("\nI/O size (bytes):\n\n");
	foreach (name in sz+) {
		printf("process name: %s\n", name);
		print(@hist_log(sz[name]));
	} 
	delete sz;
}