[gentoo-dev] Re: Request for enhancement

[Andreas Waschbuesch]

Bo Majewski wrote:

> [...]
> # If you compiled RealTek 8139 Ethernet card as a module uncomment the
> # following
> # 8139too

Let me correct this:

# If you got a RealTek 8129/8139 chip based ethernet card throw it away
# and buy a decent nic such as Intel, 3Com, DEC etc. etc.

cf. FreeBSD source: /src/sys/pci/if_rl.c

,----[ FreeBSD source: /src/sys/pci/if_rl.c ]
| $FreeBSD: src/sys/pci/if_rl.c,v 1.47 2000/10/15 14:18:59 phk Exp $
| 
| 
| RealTek 8129/8139 PCI NIC driver
| 
| Supports several extremely cheap PCI 10/100 adapters based on
| the RealTek chipset. Datasheets can be obtained from
| www.realtek.com.tw.
| 
| Written by Bill Paul <wpaul@××××××××××××.edu>
| Electrical Engineering Department
| Columbia University, New York City
| 
| 
| 
| 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.
| 
`----