Networking performance

Hi all,

I have a Sun E420R 4-way box running Solaris 8 and a dual-processor Xeon
box running Debian Sarge, kernel 2.4.27. I also have a Sun Ultra-60 on
the same LAN. All these devices are 100Mbit ethernet and are
interconnected through a 24-port 100Mbit hub.

I'm experiencing some unusual performance problems with IP comms between
the two boxes. I first noticed that there was poor NFS performance and
thought that NFS was to blame, but when I used FTP to move some files
between the machines I found problems existed through that route also.

Basically the Linux box transmits IP traffic really slowly. If I create
an empty 256MB file and attempt to FTP it from /tmp on the Linux box to
/tmp on the 420R, FTP reports that I get about 150K/sec. If I reverse
the operation and get the same 256MB file *from* the server, I get a
much more respectable 6Mbytes/sec.

If I use FTP to transmit a 256MB file from /tmp on my Ultra-60 to /tmp
on my E420R, I get 11Mbytes/sec which is what I'd expect.

Is there anything I can look at on the Linux side to explain what the
problem here seems to be ? Are there any parameters that could be
tweaked to try to correct this problem ?

Might try removing filesystems from the equation for a while and just
use netperf or ttcp. Having said that, if there is a duplex problem
that seems to manifest as perf issues in one direction but not the
other.

Sometimes, that stems from misunderstanding autoneg:

How Autoneg is supposed to work:

When both sides of the link are set to autoneg, they will "negotiate"
the duplex setting and select full duplex if both sides can do
full-duplex.

If one side is hardcoded and not using autoneg, the autoneg process
will "fail" and the side trying to autoneg is required by spec to use
half-duplex mode.

If one side is using half-duplex, and the other is using full-duplex,
sorrow and woe is the usual result.

So, the following table shows what will happen given various settings
on each side:

Auto Half Full

Auto Happiness Lucky Sorrow

Half Lucky Happiness Sorrow

Full Sorrow Sorrow Happiness

Happiness means that there is a good shot of everything going well.
Lucky means that things will likely go well, but not because you did
anything correctly Sorrow means that there _will_ be a duplex
mis-match.

When there is a duplex mismatch, on the side running half-duplex you
will see various errors and probably a number of late collisions. On
the side running full-duplex you will see things like FCS errors.
Note that those errors are not necessarily conclusive, they are simply
indicators.

If you are connecting to a real _hub_ that means half-duplex only.
However, if it is actually a _switch_ then it probably can do
full-duplex.

rick jones
--
Wisdom Teeth are impacted, people are affected by the effects of events.
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to raj in cup.hp.com but NOT BOTH...

Rick Jones wrote:
> Might try removing filesystems from the equation for a while and just
> use netperf or ttcp. Having said that, if there is a duplex problem
> that seems to manifest as perf issues in one direction but not the
> other.
>
> Sometimes, that stems from misunderstanding autoneg:

That was exactly what the problem was, an autoneg problem on the network
card. Fixed it and we're shifting bits merrily

Thanks.