[OT]Re: Well supported, reliable NICs for Redhat Linux/Fedora?
this thread is a little off-topic here. Sorry
Robert L Cochran wrote:
Xose Vazquez Perez wrote:
> A RealTek RTL-8139C+ clone is cheaper. But it must be C+, only
_8139_
> are shit. The driver is 8139cp.
I've never had a problem with any of the recent Realtek chips.
They just
work. I guess I'm using a really recent chipset!
Yes, RealTek NICs work. But RTL-8139 based has a _very_ bad design.
FreeBSD driver has more information:
/*
* 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.
* [...]
* Fast forward a few years. RealTek now has a new chip called the
* 8139C+ which at long last implements descriptor-based DMA. Not
* only that, it supports RX and TX TCP/IP checksum offload, VLAN
* tagging and insertion, TCP large send and 64-bit addressing.
* Better still, it allows arbitrary byte alignments for RX and
* TX buffers, meaning no copying is necessary on any architecture.
* There are a few limitations however: the RX and TX descriptor
* rings must be aligned on 256 byte boundaries, they must be in
* contiguous RAM, and each ring can have a maximum of 64 descriptors.
* There are two TX descriptor queues: one normal priority and one
* high. Descriptor ring addresses and DMA buffer addresses are
* 64 bits wide. The 8139C+ is also backwards compatible with the
* 8139, so the chip will still function with older drivers: C+
* mode has to be enabled by setting the appropriate bits in the C+
* command register. The PHY access mechanism appears to be unchanged.
*
[...]
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