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)