Muli Ben-Yehuda wrote:
On Thu, May 25, 2006 at 12:35:07AM -0400, Jeff Garzik wrote:
Jon Mason wrote:
>From Andi Kleen's comments on the original Calgary patch, move
valid_dma_direction into the calling functions.
Signed-off-by: Muli Ben-Yehuda <[email protected]>
Signed-off-by: Jon Mason <[email protected]>
Even though BUG_ON() includes unlikely(), this introduces additional
tests in very hot paths.
Are they really very hot? I mean if you're calling the DMA API, you're
about to frob the hardware or have already frobbed it - does this
check really matter?
When you are adding a check that will _never_ be hit in production, to
the _hottest_ paths in the kernel, you can be assured it matters...
_Why_ do we need this at all?
It was helpful for us during the dma-ops work and Calgary bringup and
Andi requested that we move it from Calgary to common code. I think
we're fine with dropping it if that's the consensus, but it did catch
a few bugs early on and the cost is tiny.
Key phrase: "early on"
These checks will only be useful during _early_ development of a new DMA
platform. For _100%_ of the real world users, these checks are useless.
Not 99%, 100%.
Jeff
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