NAME

       gethostlatency - Show latency for getaddrinfo/gethostbyname[2] calls. Uses Linux eBPF/bcc.

SYNOPSIS

       gethostlatency

DESCRIPTION

       This traces and prints when getaddrinfo(), gethostbyname(), and gethostbyname2() are called, system wide,
       and  shows  the responsible PID and command name, latency of the call (duration) in milliseconds, and the
       host string.

       This tool can be useful for identifying DNS latency, by identifying which remote host name  lookups  were
       slow, and by how much.

       This  makes  use  of  a  Linux 4.4 feature (bpf_perf_event_output()); for kernels older than 4.4, see the
       version under tools/old, which uses an older mechanism

       This  tool  currently  uses  dynamic  tracing  of  user-level  functions  and  registers,  and  may  need
       modifications to match your software and processor architecture.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -p PID Trace this process ID only.

EXAMPLES

       Trace host lookups (getaddrinfo/gethostbyname[2]) system wide:
              # gethostlatency

FIELDS

       TIME   Time of the command (HH:MM:SS).

       PID    Process ID of the client performing the call.

       COMM   Process (command) name of the client performing the call.

       HOST   Host name string: the target of the lookup.

OVERHEAD

       The rate of lookups should be relatively low, so the overhead is not expected to be a problem.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also  look  in  the bcc distribution for a companion _examples.txt file containing example usage, output,
       and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       tcpdump(8)

USER COMMANDS                                      2016-01-28                                  gethostlatency(8)