Re: RFC: FreeBSD I/OAT driver


Jack Vogel writes:
We are making our development driver for the I/OAT engine available for
download, experimentation, and comment available at:

http://sourceforge.net/project/showfiles.php?group_id=42302&package_id=202220

This includes a core driver for the dma hardware and a set of stack changes
to allow use of the engine on the receive side of the stack.

There are certainly rough edges and limitations in this code, but we have run
it internally and seen some great results.

I would like to see this get into CURRENT, so anything Prafulla and I can do
to help or answer questions, send us email.

Excellent! Can you share some of these results? I would love to try
it, but I don't have FreeBSD on any machine with I/OAT hardware.

I've taken a very quick look at it. Maybe I'm just being dense,
but I don't like the name "dma_" being in the global namespace.
Maybe things (like dma_*_list should be called at least
dmaengine_*_list, etc.

There are some style(9) defects which I'm sure others who are more
proficient at style(9) than I am will point out (// comments, function
names not starting in column 0, etc).

How deep would you expect so->dma_wait_queue to get? Would it make
sense to keep a pointer to the last item so that insertion is O(1),
rather than O(N)?

Would it be possible to have a sysctl tunable threshold, below which
the system does a normal uiomove? A normal copyout() will certainly
be faster at some point..

Thanks for the great work!

Drew





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