#!/usr/sbin/dtrace -s
/*
 * seeksize.d - analyse disk head seek distance by process.
 *              Written using DTrace (Solaris 10 3/05).
 *
 * Disk I/O events caused by processes will in turn cause the disk heads
 * to seek. This program analyses those seeks, so that we can determine
 * if processes are causing the disks to seek in a "random" or "sequential"
 * manner.
 *
 * 15-Jun-2005, ver 1.00
 *
 * USAGE:	seeksize.d		# wait several seconds, then hit Ctrl-C
 *
 * FIELDS:
 *		PID	process ID
 *		CMD	command and argument list
 *		value	distance in disk blocks (sectors)
 *		count	number of I/O operations
 *
 * SEE ALSO: bitesize.d, iosnoop
 *
 * Standard Disclaimer: This is freeware, use at your own risk.
 *
 * 11-Sep-2004	Brendan Gregg	Created this.
 * 10-Oct-2004	   "      "	Rewrote to use the io provider.
 */

#pragma D option quiet

/*
 * Print header
 */
dtrace:::BEGIN
{
	printf("Sampling... Hit Ctrl-C to end.\n");
}

self int last[dev_t];

/*
 * Process io start
 */
io:::start
{
	/* fetch details */
	this->dev = args[0]->b_edev;
	this->blk = args[0]->b_blkno;
	this->size = args[0]->b_bcount;
	cmd = (string)curpsinfo->pr_psargs;
}
io:::start
/self->last[this->dev] != 0/
{
	/* calculate seek distance */
	this->dist = this->blk - self->last[this->dev] > 0 ?
	    this->blk - self->last[this->dev] :
	    self->last[this->dev] - this->blk;

	/* store details */
	@Size[pid,cmd] = quantize(this->dist);
}
io:::start
{
	/* save last position of disk head */
	self->last[this->dev] = this->blk + this->size / 512;
}

/*
 * Print final report
 */
dtrace:::END 
{
	printf("\n%8s  %s\n","PID","CMD");
	printa("%8d  %s\n%@d\n",@Size);
}