Roland Dreier wrote:
> I see. Just wondering, in the mlx4 case, is it a must to use dma
> consistent memory allocation or dma mapping would work too?
dma mapping would work too but then handling the map/unmap becomes an
issue. I think it is way too complicated too add new verbs for
map/unmap fastreg page list (in addition to the alloc/free fastreg page
list that we are already adding) and force the consumer to do it. And
if we expect the low-level driver to do it, then the map is easy (can be
done while posting the send) but the unmap is a pain -- it would have to
be done inside poll_cq when reapind the completion, and the low-level
driver would have to keep some complicated extra data structure to go
back from the completion to the original fast reg page list structure.
And certain platforms can fail map requests (like PPC64) because they
have limited resources for dma mapping. So then you'd fail a SQ work
request when you might not want to...
Steve.
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