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Performance of IOMemoryDescriptor::prepare on contiguous, wired memory

Lets say I do the following:

- IOMallocContiguous some memory in a driver
- map this memory to a user process
- change the (entire) contents of the memory (in the user process)
- pass the user address to a (different) driver
- create an IOMemoryDescriptor for this user address
- call IOMemoryDescriptor->prepare
- call IOMemoryDescriptor->getPhysicalAddress
- do some DMA

Since I know the memory is contiguous and wired, I had expected prepare()
to be very fast. However, it sometimes takes up to 11 ms (Dual 450 G4)!
Is my expectation of prepare() invalid? Is it safe to not call prepare
(yet call getPhysicalAddress) when I know the memory is contiguous and wired?

Thanks for any insight!

--
____________________________________________________________
Sean McBride, B. Eng email@hidden
Mac Software Designer +1-514-822-6000 x7399
Matrox Electronic Systems Ltd. Montrial, Quibec, Canada
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