tigon3: 2466 and bad performance at 32bits/33mhz ?

tigon3: 2466 and bad performance at 32bits/33mhz ?

[Robert Latham]

I've got a 3com 3C996B-T (copper) and a tyan 2466 motherboard.  The
kernel is 2.4.19-rc1-ac2, and i'm using the tg3 v0.99 (Jun 11, 2002).

When i run the 3C996B-T in the 64-bit/66-MHz slot, i get great
performance.  When i run the card in the 32-bit/66-MHz slot, i get
pretty bad performance.  Here's a netpipe graph to demonstrate:

http://www-unix.mcs.anl.gov/~robl/storage_box/tg3-32_33.2.png

The fast curve is with the 3c996B-T in the 64/66 slot.  It peaks out
around 850 Mbps.  The slow curve is the same card in the 32/33 slot.
It peaks around 180 Mbps.

Is a maximum throughput of ~180 MBits/sec all that can be hoped for?  I
don't have the hardware to verify, but 
http://www.cs.uni.edu/~gray/gig-over-copper/#3Com%203c996BT:|outline
offers the datapoint of 436 MBits/sec in an oldish dell optiplex ( old
being whenever p3 500 mhz machines were still made)

So, am i looking at a hardware limitation?  driver quirk?  I'm open to
any suggestions.  

I'll keep an eye on the web archives, but please CC me on any replies.

thanks
==rob

-- 
Rob Latham
Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
Argonne National Labs, IL USA                B29D F333 664A 4280 315B

Re: tigon3: 2466 and bad performance at 32bits/33mhz ?

[Willy Tarreau]

On Tue, Aug 06, 2002 at 12:35:08AM -0500, Robert Latham wrote:
> The fast curve is with the 3c996B-T in the 64/66 slot.  It peaks out
> around 850 Mbps.  The slow curve is the same card in the 32/33 slot.
> It peaks around 180 Mbps.
[snip]
> So, am i looking at a hardware limitation?  driver quirk?  I'm open to
> any suggestions.  

on a 32/33 slot, with a quad fast ethernet card, I can reach 400 Mbps
on good hardware. The *theorical* bandwidth limit is 1.06 Gbps for
32 bits/33 Mhz. Of course, there's some overhead, but you would need 80%
overhead to get you numbers, not very likely...

Perhaps this slot is on another bus, perhaps the latency timer is too
low and the card receives small chunks at once, or perhaps this bus
is shared with another hungry device ?

Regards,
willy

Re: tigon3: 2466 and bad performance at 32bits/33mhz ?

[Ben Greear]

Willy Tarreau wrote:
> On Tue, Aug 06, 2002 at 12:35:08AM -0500, Robert Latham wrote:
> 
>>The fast curve is with the 3c996B-T in the 64/66 slot.  It peaks out
>>around 850 Mbps.  The slow curve is the same card in the 32/33 slot.
>>It peaks around 180 Mbps.
> 
> [snip]
> 
>>So, am i looking at a hardware limitation?  driver quirk?  I'm open to
>>any suggestions.  
> 
> 
> on a 32/33 slot, with a quad fast ethernet card, I can reach 400 Mbps
> on good hardware. The *theorical* bandwidth limit is 1.06 Gbps for
> 32 bits/33 Mhz. Of course, there's some overhead, but you would need 80%
> overhead to get you numbers, not very likely...
> 
> Perhaps this slot is on another bus, perhaps the latency timer is too
> low and the card receives small chunks at once, or perhaps this bus
> is shared with another hungry device ?
> 
> Regards,
> willy

I'm pushing 650Mbps on a 32/33 PCI bus using a Netgear GA620 GigE
card (the card supports 64bit PCI).  So, its not exactly a PCI bus
limitation you are hitting unless your PCI chipset somehow really
sucks.

Ben

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-- 
Ben Greear <greearb@candelatech.com>       <Ben_Greear AT excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear