poor PCMCIA network performance

[mark at buttery.org (Mark J. Dulcey)]

Robert L Krawitz wrote:
> I use two network cards in my Dell Inspiron 8000 (PIII-700): a 3Com
> 3CCFE574BT and a Linksys wireless card.  With the 3Com card (which is
> a 10/100) I never get better than 1.4 MB/sec (about 12 Mb/sec), even
> when the card is in 100 Mb mode (at some point in the past the limit
> was about 2.5 MB/sec).  At that rate, top shows my CPU utilization
> pegged at about 100%, even doing a simple ftp.  I know the card
> doesn't do DMA, but that's rather slow even for a PIO transfer.  These
> cards have been around for ages; I don't think people would have been
> too satisfied with 400 KB/sec saturating a 200 MHz system.

Your results with the 3Com card are normal for a 16-bit PCMCIA card. The 
wall you're hitting is the PCMCIA interface. You would have done much 
better to get a CardBus card (such as the 3CCFE575CT); you should be 
able to saturate a Fast Ethernet with one of those, and the CPU 
utilization would be lower.

Basically, 10/100 16-bit cards are something of a lie, since you can 
never get anywhere near 100 Mbps from them. The same is true of 10/100 
USB interfaces (the 12 Mbps speed of USB is a hard limit), though USB 
2.0 (480 Mbps) could be different if anyone ever produces a USB 2.0 
Ethernet interface.

> On the Linksys card, I likewise never get more than about 250 KB/sec,
> even if the computer is right next to the WAP and the link quality is
> 92/92, suggesting that I'm also hitting up against a hard limit.  The
> WAP is connected to my main system via the motherboard ethernet, which
> I know from other means (when I was transferring data from my previous
> system to the current one) has no trouble maxing out at 10 MB/sec
> (that ethernet does DMA).

Not sure about that one; it may be that you're doing about as well as 
802.11b and your access point will allow. The bit rate of 802.11b is 
11Mbps, but there are other issues with wireless, such as latency 
(always higher than wired LANs) and delays for the collision avoidance.