gethostlatency.bt

#!/usr/bin/env bpftrace
// gethostlatency	Trace getaddrinfo/gethostbyname[2] calls.
// 			For Linux, uses bpftrace and eBPF.
//
// This can be useful for identifying DNS latency, by identifying which
// remote host name lookups were slow, and by how much.
//
// This uses dynamic tracing of user-level functions and registers, and may
// need modifications to match your software and processor architecture.
//
// Example of usage:
//
// # ./gethostlatency.bt
// Attaching 7 probes...
// Tracing getaddr/gethost calls... Hit Ctrl-C to end.
// TIME      PID    COMM              LATms HOST
// 02:52:05  19105  curl                 81 www.netflix.com
// 02:52:12  19111  curl                 17 www.netflix.com
// 02:52:19  19116  curl                  9 www.facebook.com
// 02:52:23  19118  curl                  3 www.facebook.com
//
// In this example, the first call to lookup "www.netflix.com" took 81 ms, and
// the second took 17 ms (sounds like some caching).
//
// This is a bpftrace version of the bcc tool of the same name.
// The bcc version provides options to customize the output.
//
// Copyright 2018 Netflix, Inc.
//
// 08-Sep-2018	Brendan Gregg	Created this.

config = {
  missing_probes = ignore;
}

BEGIN
{
  printf("Tracing getaddr/gethost calls... Hit Ctrl-C to end.\n");
  printf("%-9s %-6s %-16s %6s %s\n", "TIME", "PID", "COMM", "LATms", "HOST");
}

uprobe:libc:gethostbyaddr,
uprobe:libc:gethostbyaddr_r
{
  @start[tid] = nsecs;
  @inet[tid] = ntop(arg0);
}

uprobe:libc:getaddrinfo,
uprobe:libc:gethostbyname,
uprobe:libc:gethostbyname_r,
uprobe:libc:gethostbyname2,
uprobe:libc:gethostbyname2_r
{
  @start[tid] = nsecs;
  @name[tid] = arg0;
}

macro print_result(start, name)
{
  $latms = (nsecs - start) / 1e6;
  time("%H:%M:%S  ");
  printf("%-6d %-16s %6d %s\n", pid, comm, $latms, name);
}

uretprobe:libc:getaddrinfo,
uretprobe:libc:gethostbyname,
uretprobe:libc:gethostbyname_r,
uretprobe:libc:gethostbyname2,
uretprobe:libc:gethostbyname2_r
/@start[tid]/
{
  print_result(@start[tid], str(@name[tid]));
  delete(@start, tid);
  delete(@name, tid);
}

uretprobe:libc:gethostbyaddr,
uretprobe:libc:gethostbyaddr_r
/@start[tid]/
{
  print_result(@start[tid], @inet[tid]);
  delete(@start, tid);
  delete(@inet, tid);
}

END
{
  clear(@name);
  clear(@inet);
}