loads.bt

#!/usr/bin/env bpftrace
/*
 * loads	Prints load averages.
 *		For Linux, uses bpftrace and eBPF.
 *
 * These are the same load averages printed by "uptime", but to three decimal
 * places instead of two (not that it really matters). This is really a
 * demonstration of fetching and processing a kernel structure from bpftrace.
 *
 * USAGE: loads.bt
 *
 * This is a bpftrace version of a DTraceToolkit tool.
 *
 * Copyright 2018 Netflix, Inc.
 * Licensed under the Apache License, Version 2.0 (the "License")
 *
 * 10-Sep-2018	Brendan Gregg	Created this.
 */

BEGIN
{
	printf("Reading load averages... Hit Ctrl-C to end.\n");
}

interval:s:1
{
	/*
	 * See fs/proc/loadavg.c and include/linux/sched/loadavg.h for the
	 * following calculations.
	 */
	$avenrun = kaddr("avenrun");
	$load1 = *$avenrun;
	$load5 = *($avenrun + 8);
	$load15 = *($avenrun + 16);
	time("%H:%M:%S ");
	printf("load averages: %d.%03d %d.%03d %d.%03d\n",
	    ($load1 >> 11), (($load1 & ((1 << 11) - 1)) * 1000) >> 11,
	    ($load5 >> 11), (($load5 & ((1 << 11) - 1)) * 1000) >> 11,
	    ($load15 >> 11), (($load15 & ((1 << 11) - 1)) * 1000) >> 11
	);
}