RE: TCP Segmentation Offloading (TSO)

["Jordi Ros" <jros@ece.uci.edu>]

One question regarding the throughput numbers,

what was the size of the packets built at the tcp layer (mss)?

i assume the mtu is ethernet 1500 Bytes, right? and that mss should be
something much bigger than mtu, which gives the performance improvement
shown in the numbers.

thanks,

jordi

-----Original Message-----
From: linux-net-owner@vger.kernel.org
[mailto:linux-net-owner@vger.kernel.org]On Behalf Of Feldman, Scott
Sent: Monday, September 02, 2002 10:45 AM
To: linux-kernel@vger.kernel.org; linux-net; 'Dave Hansen';
'Manand@us.ibm.com'
Cc: kuznet@ms2.inr.ac.ru; 'David S. Miller'; Leech, Christopher
Subject: TCP Segmentation Offloading (TSO)


TCP Segmentation Offloading (TSO) is enabled[1] in 2.5.33, along with an
enabled e1000 driver.  Other capable devices can be enabled ala e1000; the
driver interface (NETIF_F_TSO) is very simple.

So, fire up you favorite networking performance tool and compare the
performance gains between 2.5.32 and 2.5.33 using e1000.  I ran a quick test
on a dual P4 workstation system using the commercial tool Chariot:

Tx/Rx TCP file send long (bi-directional Rx/Tx)
  w/o TSO: 1500Mbps, 82% CPU
  w/  TSO: 1633Mbps, 75% CPU

Tx TCP file send long (Tx only)
  w/o TSO: 940Mbps, 40% CPU
  w/  TSO: 940Mbps, 19% CPU

A good bump in throughput for the bi-directional test.  The Tx-only test was
already at wire speed, so the gains are pure CPU savings.

I'd like to see SPECWeb results w/ and w/o TSO, and any other relevant
testing.  UDP framentation is not offloaded, so keep testing to TCP.

-scott

[1] Kudos to Alexey Kuznetsov for enabling the stack with TSO support, to
Chris Leech for providing the e1000 bits and a prototype stack, and to David
Miller for consultation.
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