Before tweaks
=============

Standard installations, no intentional tweaks despite "UseDNS no". All
VMs run on the same host using KVM.


Arch Linux (openssh-6.8p1-2):

    $ time for i in {1..100}; do ssh overqemu00 /bin/true; done

    real    0m9.904s
    user    0m1.300s
    sys     0m0.123s


Ubuntu 12.04 (openssh-server-5.9p1-5ubuntu1.4):

    $ time for i in {1..100}; do ssh overqemu01 /bin/true; done

    real    0m34.388s
    user    0m0.797s
    sys     0m0.130s


Ubuntu 14.04 (openssh-server-6.6p1-2ubuntu2):

    $ time for i in {1..100}; do ssh overqemu02 /bin/true; done

    real    0m32.895s
    user    0m1.340s
    sys     0m0.133s


CentOS 7 (openssh-6.6.1p1-11.el7):

    $ time for i in {1..100}; do ssh overqemu05 /bin/true; done

    real    0m18.580s
    user    0m1.093s
    sys     0m0.133s



For further reference:

OpenBSD 5.6 (openssh-6.7):

    $ time for i in {1..100}; do ssh overqemu03 /usr/bin/true; done

    real    0m8.871s
    user    0m1.293s
    sys     0m0.113s


FreeBSD 10.1 (openssh-6.6.1p1):

    $ time for i in {1..100}; do ssh overqemu04 /usr/bin/true; done

    real    0m8.876s
    user    0m1.483s
    sys     0m0.200s



After tweaks
============

What has been changed?

    - Cleared /etc/update-motd.d on Ubuntu. PAM runs all these scripts
      on each login.


Ubuntu 12.04:

    $ time for i in {1..100}; do ssh overqemu01 /bin/true; done

    real    0m6.884s
    user    0m0.850s
    sys     0m0.170s


Ubuntu 14.04:

    $ time for i in {1..100}; do ssh overqemu02 /bin/true; done

    real    0m8.452s
    user    0m1.490s
    sys     0m0.187s