Performance improvement in OpenSSH 4.0

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I am impressed to see a considerable performance improvement in file
transfers after upgrading my system to OpeSSH 4.0( running on HP-UX). I
measured the time taken to scp ( using host based authentication ) a
file of 40 MB through 100 mbps local network, on average it is

OpenSSH 3.9 : 4.22 secs
OpenSSH 4.0 : 4.15 secs

(measured with 'time' command )

Jus curious to know that any performance enhancement is incorparated in
OpenSSH 4.0 and Is there any addtional ways to improve the performance
to save the time.

Advanced thanks for all your views.

Re: Performance improvement in OpenSSH 4.0

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Some changes were made to the buffer code so large buffers are utilized

If you're particularly curious you could feed this diff into patch -R,
recompile and see if the performance improvement goes away:

If you haven't already, try speed-testing other ciphers (of the standard
ciphers, arcfour is usually the fastest with blowfish second).

For additional improvements you could try the HPN patch: /

Darren Tucker (dtucker at
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.

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