RFC: FreeBSD I/OAT driver

[Andrew Gallatin]

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