[realtek] What throughput can be expected

Donald Becker becker@scyld.com
Mon Jan 7 12:48:01 2002

On Mon, 7 Jan 2002, Ambrus Michael wrote:

> I'm having problems getting the throughput up on my recently upgraded home
> LAN. The NIC's "non-branded" but PCI based with the RTL8139 chip. I'm
> getting roughly 1.2MB/s on a LAN where the two clients used for the tests
> are the only ones connected. The machines are P166 and AMD450 based.

The packet copying required with the rtl8139 will have a significant
impact with the P166 macine.

> I've calculated the statistics simply by transferring large files with (only
> a few however) application protocols - NFS and Samba. There seems not to be
> a great difference in performance.

Use 'ttcp' to test the TCP performance.  Transferring files adds a bunch
of other issues to the test.

> Since I'm quite new to FastEthernet my questions are as follows:
> * What throughput can be expected both in general for FastEthernet and
> specifically for RTL8139 based NIC's

TCP Fast Ethernet: 10.9-11.5 MB/sec using the measurement of 'ttcp'.
(TTCP counts only data payload bytes, and uses MB == 2^20, not 10^6.)

> * Where can I expect to find the bottle-necks (please elaborate if
> possible).

The extra copying copy of packets to and from the memory used by the
rtl8139, and various overheads depending on the kernel version.  The 2.0
kernels were more efficient that the 2.2 and 2.4 kernels.

> * I'm not using the most up-to-date driver, but I think the one that comes
> with RH7.1 should be recent enough?

The driver issues are almost always in dealing with media selection and
error recovery.  The core packet transfer code has not changed.

> * Is there a utility for managing the NIC EEPOROM without having to do it
> from DOS?


[[ This has been mentioned many times, and is on the rtl8139 page. ]]

> * Can you get 200MB/s full-duplex with a hub-based LAN or do you need a
> switch for this?

You need a switch to direct connect to use full duplex.  For typical
workstation traffic you will see a 3-4% performance improvement.  The
"200Mbps" (not MBps, it's Mbps) is marketing nonsense.

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993