Screw you Realtek

Around the turn of the century, I consulted FreeBSD's if_rl.c when writing a driver for the RTL8139c:

The Realtek 8139 PCI NIC redefines the meaning of 'low end.' This is probably the worst PCI ethernet controller ever made, with the possible exception of the FEAST chip made by SMC. The 8139 supports bus-master DMA, but it has a terrible interface that nullifies any performance gains that bus-master DMA usually offers.

For transmission, the chip offers a series of four TX descriptor registers. Each transmit frame must be in a contiguous buffer, aligned on a longword (32-bit) boundary. This means we almost always have to do mbuf copies in order to transmit a frame, except in the unlikely case where a) the packet fits into a single mbuf, and b) the packet is 32-bit aligned within the mbuf's data area. The presence of only four descriptor registers means that we can never have more than four packets queued for transmission at any one time.

Reception is not much better. The driver has to allocate a single large buffer area (up to 64K in size) into which the chip will DMA received frames. Because we don't know where within this region received packets will begin or end, we have no choice but to copy data from the buffer area into mbufs in order to pass the packets up to the higher protocol levels.

It's impossible given this rotten design to really achieve decent performance at 100Mbps, unless you happen to have a 400Mhz PII or some equally overmuscled CPU to drive it.

The author had expressed my feelings better than I ever could. And I'm smiling, right now, because after all these years that expression still has a home in FreeBSD's main.

7372 (0x1CCC) s a really odd number to cause issues here, no?

What a needlessly hard-to-read website.