Paul Durrant wrote:
Mark Johnson wrote:
Why not put it in the DDI? There's nothing GLD specific about DMA.
Who else would use it besides NICs?
Who knows? I just don't see any point in trying to be restrictive
though. STREAMS blocks and associated functions are part of the DDI so
why not provide DMA mapping functions specific to them in the DDI?
The diversity of NIC h/s is the reason why the goal of common
codepath optimization is probably not realistic. I've come across
many NIC drivers and the schemes for driving different chips is
usually too diverse; it would be possible to make code common but it
would just be equally bad on all chips.
I certainly can see difficulties on the rx side. It would
be interesting to hear about a case which was a one off one
though.. I would imagine you would be able to bin most of
them.
My driver has relatively complex receive path because I do LRO in s/w.
certainly if you combining RX buffers, etc... You wouldn't want
to use common rx buffer code.. :-)
But I don't think that is the 90% case? (i.e. you would
never be forced to use it). I would expect 10G NICs
to be custom in the near term..
Thus I have to maintain flow tables and coalescing state; I agree that
this code looks like a candidate for making common but my h/w generates
a hash which can be used to optimize flow lookup; can that be made
common? Also, code placement causing i-cache misses turned out to be
significant and I even went to the trouble of using some pretty
cumbersom macros to try to tune out function call overhead; can that be
made common?
I'd be interested in examples on the TX side where this
is the case.
Commonality on the TX side could be defeated by fragmentation rules.
Soft LSO would seem like a a good thing to make common but can you do it
in such a way that can handle h/w with a restriction that fragments not
aligned on a 16 byte boundary cannot exceed 512 bytes in length? (Yes,
the h/w is broken but show me a piece of h/w that is not). A driver
writer's job is to cover up mistakes in h/w design :-)
I agree about the HW broken comment :-) But I'm not sure how
you are restricted by getting a scatter/gather list passed
down to the driver too.. i.e. you have the VA, size, and SGL.
If you need to carve up the SGL, then go for it.
MRJ
Paul
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