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.
//
// Example of usage:
//
// # ./loads.bt
// Attaching 2 probes...
// Reading load averages... Hit Ctrl-C to end.
// 21:29:17 load averages: 2.091 2.048 1.947
// 21:29:18 load averages: 2.091 2.048 1.947
// 21:29:19 load averages: 2.091 2.048 1.947
// 21:29:20 load averages: 2.091 2.048 1.947
// ^C
//
// These are the same load averages printed by uptime:
//
// # uptime
//  21:29:24 up 2 days, 18:57,  3 users,  load average: 2.16, 2.06, 1.95
//
//
// For more on load averages, see the post:
// http://www.brendangregg.com/blog/2017-08-08/linux-load-averages.html
//
// This is a bpftrace version of a DTraceToolkit tool.
//
// Copyright 2018 Netflix, Inc.
//
// 10-Sep-2018	Brendan Gregg	Created this.

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

interval:1s
{
  // 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);
}