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Tech Support Getting Even Worse
ehiris writes: "Came across an article on CNN about tech support falling out of the useful category. The interesting quote: 'In part, the problem can be blamed on tech companies' attempts to cope with shrinking profit margins and a bad business environment.' Bad tech support makes life hard and new technology becomes undesirable to the general public. Which company has the best support? What are they doing well? What would you like to see improve about tech support?"
Damn I hate calling tech support and giving the people on the other end a lesson on whatever it is they are supposed to help me out with. Whose providing the tech support? They caller or the call center!!!!
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.
On the bright side, the 8139 does have a built-in PHY, although rather than using an MDIO serial interface like most other NICs, the PHY registers are directly accessible through the 8139's register space. The 8139 supports autonegotiation, as well as a 64-bit multicast filter.
The 8129 chip is an older version of the 8139 that uses an external PHY chip. The 8129 has a serial MDIO interface for accessing the MII where the 8139 lets you directly access the on-board PHY registers. We need to select which interface to use depending on the chip type. ~