[realtek] 8139too performance - can you shed some light?

Ben Greear greearb@candelatech.com
Wed, 01 Aug 2001 15:00:17 -0700

"Carlo E. Prelz" wrote:
> Hello gurus.
> My situation: I have to use optimally a 100MB network for transferring
> multimedia material from a master machine to multiple single-board
> computers.

See if you can tell where the pkts are being dropped, and for what
reason.  Take a look at the /proc/net/dev file on all the machines,
for instance.  You can also increase the kernel buffers for sockets.  If you do a
netstat -an | grep udp, then you can see your current buffer usage,
and that may give you some ideas.  Do that many times because the buffers
fill and un-fill quickly.  Finally, you can try increasing
the driver TX buffers.

Check to make sure you are running at 100bt-FD too...

I have some more detailed information in my FAQ on www.candelatech.com.
It's primarily geared towards my application, but the general ideas may
be useful to you...

Btw, I've had very good luck with Intel 82557+ NICs, but they are definately
more expensive...


> All computers run with kernel 2.4.7.
> The SBC's are powered by a NatSemi Geode CPU (Pentium-MMX class, the
> core is Cyrix) @ 233MHz, have 32MB of memory and are equipped with a
> RTL-8139C chip:
> --8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<--
> eth0: RealTek RTL8139 Fast Ethernet at 0xc2a14000, 00:d0:c9:34:97:73, IRQ 15
> eth0:  Identified 8139 chip type 'RTL-8139C'
> NET4: Linux TCP/IP 1.0 for NET4.0
> IP Protocols: ICMP, UDP, TCP, IGMP
> IP: routing cache hash table of 512 buckets, 4Kbytes
> TCP: Hash tables configured (established 2048 bind 2048)
> eth0: Setting 100mbps full-duplex based on auto-negotiated partner ability 41e1.
> --8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<--
> I equipped the master machine with two very cheap netcards, that have the
> same chip (equal lines at boot time), one for connecting with the
> world and the second for communications with the cluster of SBCs.
> Needing to provide the same data to all machines, I used multicast,
> and UDP. I wrote a simple protocol where I can easily change the
> packet size.
> At the beginning of the development, before I obtained the master
> machine, I developed on my home machine, talking with the SBC from a
> PCI ne2000-compatible card at 10Mbps, via my cheap 4-port hub. All
> went OK, with the slow rate that I expected would be multiplied by 10
> with the upgrade to 100Mbps.
> I set up the master machine, and its second ethernet card has been
> connected to the SBC's port with a crossover cable. Normal TCP stuff
> (mainly ssh) works perfectly.
> When I tested my UDP software, I discovered with dismay that most of
> the packets disappeared: they were not even registered by tcpdump on
> the SBC.
> I was able to reduce the packet loss to 0 by checking the output queue
> on the server side with ioctl (SIOCOUTQ) and only sending when the
> queue size dropped under a certain level. But then, the rate of
> transmission was eventually comparable with what I obtained with
> 10Mbps.
> While communications is just barely able to maintain its error-free
> state (showing that some kind of bottleneck is reached) I can chat
> with the SBC via ssh observing little or no delay.
> I tried to:
> - change RX_BUF_LEN_IDX to 3
> - set parameter "Use PIO instead of MMIO" in kernel config
> In both cases, the driver would refuse to operate.
> I changed max_interrupt_work from 20 to 30 and then 60, without
> appreciable changes.
> I twiddled with some parameters in /proc/sys/net, also without
> appreciable changes.
> I know that UDP has no assurance to deliver packets, so I expected to
> lose one packet here and there, but to lose the great majority of
> packets, and all this on a direct crossover cable (trying 3 different
> cables, too) is a bit of an anticlimax.
> My questions are:
> - Did I do some stupid, evident blunder? What can my current
> bottleneck be?
> - What throughput can I expect from a 1-way UDP traffic between two
> 8139C's (and eventually, to a bunch of them on a hub/switch)?
> - Do I need to change the hardware? I know that the 8139 chip is
> cheap...
> Thanks in advance. I can provide other info if requested.
> Carlo Prelz
> --
>   *         Se la Strada e la sua Virtu' non fossero state messe da parte,
> * K * Carlo E. Prelz - fluido@fluido.as             che bisogno ci sarebbe
>   *               di parlare tanto di amore e di rettitudine? (Chuang-Tzu)
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Ben Greear <greearb@candelatech.com>          <Ben_Greear@excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear