Garrett D'Amore writes:

 > NICs do this, although practical experience has shown that on modern 
 > hardware the cost of setup and tear down for zero copy (direct DMA) 
 > costs more than it takes to just bcopy an ethernet size frame.  (Jumbo 
 > Frames are entirely a different story, however.)

In my experience, this is true only on sparc, and even then only when
DDI_DMA_FORCE_PHYSICAL isn't available (eg, you need to go through the
pain and suffering of the iommu setup/teardown for each mapping).

Drew
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