Andi Kleen wrote:
On Thursday 25 May 2006 11:58, Jeff Garzik wrote:
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...
pci_dma_* shouldn't be that hot. Or at least IO usually has so much
overhead that some more bugging shouldn't matter.
I respectfully disagree with that logic. If its a key hot path -- which
it is, every modern network or disk I/O runs through these paths -- then
it deserves at least _some_ consideration before adding more CPU cycles.
On the other hand if the problem of passing wrong parameters here
isn't common I would be ok with dropping them.
As the author noted, it was only used in early platform bring-up. And
simply reviewing the patch... it is clear that screwing up the
parameters would cause massive, noticeable problems immediately -- such
as on EM64T with swiotlb.
Jeff
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