tools/tcpsynbl_example.txt

Demonstrations of tcpsynbl, the Linux BCC/eBPF version.


This tool shows the TCP SYN backlog size during SYN arrival as a histogram.
This lets you see how close your applications are to hitting the backlog limit
and dropping SYNs (causing performance issues with SYN retransmits). For
example:

# ./tcpsynbl.py 
Tracing SYN backlog size. Ctrl-C to end.
^C

backlog_max = 500L
     backlog             : count     distribution
         0 -> 1          : 961      |****************************************|
         2 -> 3          : 1        |                                        |

This output shows that for the backlog limit of 500, there were 961 SYN
arrival where the backlog was zero or one, and one accept where the backlog was
two or three. This indicates that we are nowhere near this limit.

USAGE:

# ./tcpsynbl -h
usage: tcpsynbl.py [-h] [-4 | -6]

Show TCP SYN backlog.

optional arguments:
  -h, --help  show this help message and exit
  -4, --ipv4  trace IPv4 family only
  -6, --ipv6  trace IPv6 family only

examples:
    ./tcpsynbl          # trace syn backlog
    ./tcpsynbl -4       # trace IPv4 family only
    ./tcpsynbl -6       # trace IPv6 family only