Odd ethnetnet problem

Odd ethnetnet problem

[bob]

I have an iMac with the usual builtin  bmac ethernet controller. It is on a 
10 mb hup with a couple of other boxes (one professional svr4 and one linux
2.2.10 on intel)

The hub is a generic dumb 10mb half duplex only unit. The problem is this,

When the iMac talked to either Unix box from MACOS, I would get
nearly 100% of the bandwidth of the ethernet on put's and get's.

When the iMac talked to either Unix box from linux-ppc (several kernels
tested), I would get nearly 100 percent on receive but REALLY slow
response on transmit (like about 40k/sec). Watching the lights on the hub,
it appears that there is a really big delay restarting transmit after
a collision occurs. Perhaps duplex set wrong?

Since it works fine in MACOS, I looked over the linux driver and didn't see
anything obviously wrong. Has anyone else run into this before? 

Bob
-- 
Robert E. Brose II    N0QBJ
http://www.jriver.com/~bob/
bob@kunk.jriver.com

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Re: Odd ethnetnet problem

[Paul Mackerras]

bob@kunk.jriver.com wrote:

> When the iMac talked to either Unix box from linux-ppc (several kernels
> tested), I would get nearly 100 percent on receive but REALLY slow
> response on transmit (like about 40k/sec). Watching the lights on the hub,
> it appears that there is a really big delay restarting transmit after
> a collision occurs. Perhaps duplex set wrong?

I have seen this too but I haven't figured out what's going wrong yet.
My suspicion is that some packets are getting corrupted somehow on
transmission and then we are having to wait for a TCP retransmit.  A
tcpdump might yield some interesting information.

Paul.

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Re: Odd ethernet problem

[bob]

User Paul Mackerras says:
> bob@kunk.jriver.com wrote:
> 
> > When the iMac talked to either Unix box from linux-ppc (several kernels
> > tested), I would get nearly 100 percent on receive but REALLY slow
> > response on transmit (like about 40k/sec). Watching the lights on the hub,
> > it appears that there is a really big delay restarting transmit after
> > a collision occurs. Perhaps duplex set wrong?
> 
> I have seen this too but I haven't figured out what's going wrong yet.
> My suspicion is that some packets are getting corrupted somehow on
> transmission and then we are having to wait for a TCP retransmit.  A
> tcpdump might yield some interesting information.
> 
> Paul.

Good suggestion, I'll setup a tcp dump and check it out. I did try hacking
the transmit timer without success...

Bob

-- 
Robert E. Brose II    N0QBJ
http://www.jriver.com/~bob/
bob@kunk.jriver.com

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Re: Odd iMac ethernet problem

[bob]

User Paul Mackerras says:
> bob@kunk.jriver.com wrote:
> 
> > When the iMac talked to either Unix box from linux-ppc (several kernels
> > tested), I would get nearly 100 percent on receive but REALLY slow
> > response on transmit (like about 40k/sec). Watching the lights on the hub,
> > it appears that there is a really big delay restarting transmit after
> > a collision occurs. Perhaps duplex set wrong?
> 
> I have seen this too but I haven't figured out what's going wrong yet.
> My suspicion is that some packets are getting corrupted somehow on
> transmission and then we are having to wait for a TCP retransmit.  A
> tcpdump might yield some interesting information.

I haven't got tcpdump setup on another linux box yet but I did borrow a 
10/100 NWay switch from work and tested the 4 speed/duplex combinations.

The iMac transmits properly only on 100mb/half duplex (860 k/sec, it's
talking to a redhat i386 linux box on 10mb on another switch port).
All the rest of the combinations are 60k/sec or less on transmit.

Hopefully I'll have time to do a packet trace this evening.

Bob
-- 
Robert E. Brose II    N0QBJ
http://www.jriver.com/~bob/
bob@kunk.jriver.com

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