Subject: Re: Intel i82547 performance problems in wm(4)
To: Jonathan Stone <>
From: Mipam <>
List: tech-net
Date: 07/19/2004 17:14:28

> There are many ways in which card designers can (and have) gotten
> their checksum-offload implementation wrong. There is also the
> possibilty that errors will occur after the offloaded checksum -- for
> example, due to hardware errors which are "outside" the coverage of
> the outboard checksum (e.g., a soft memory failure in internal NIC
> buffers, a glitch in an on-chip FIFO, etc).
> The Large Vendors selling into the server market seem to've gotten the
> systemic bugs out of their offload implementations. OTOH, checksum
> offload is now down to ~$20 NICs.  Personally (and after finding such
> FIFO bugs, in several low-end NICs), I'd think very, very hard before
> enabling checksum offload on such low-end NICs, on any system moving
> data I cared about.
> Ask yourself, how exhaustive a QA effort is the vendor really likely
> to do, at that price?  Will they, for example, make the effort to put
> parity on their internal NIC buffers?  Will they force an NMI if they
> do detect an error?
> OTOH, look at the checksum-offload-bug-workarounds in our
> sys/dev/if_bge.c: which I'd probably now trust, in the sense that
> undetected errors in, or outside checksum offload (errors that would
> be detected by an end-to-end software TCP checksum) are less likely
> than errors elsewhere.

I have been wondering as well how well csum offloading is actually 
going on and about bugs in the firmware. What kind of cards have good 
offloading implementations? For example the intel pro/1000MT nic also 
supports offloading, does it do this nicely or at least better then 
Many dell and compaq systems seem to come nowadays with broadcom cards 
onboard, on high load server i replace them by intel cards by default to 
have better network performance. I dont know about the experience upon 
this by others, but it's just how i experienced working with bge cards.