On 7/23/2015 8:55 PM, Jason Gunthorpe wrote:
On Thu, Jul 23, 2015 at 01:15:16PM +0300, Sagi Grimberg wrote:
I was hoping we'd move the DMA flush and translate into here and make
it mandatory. Is there any reason not to do that?
The reason I didn't added it in was so the ULPs can make sure they meet
the restrictions of ib_map_mr_sg(). Allow SRP to iterate on his
SG list set partials and iSER to detect gaps (they need to dma map
for that).
The ULP can always get the sg list's virtual address to check for
gaps. Page aligned gaps are always OK.
So I had a go with moving the DMA mapping into ib_map_mr_sg() and
it turns out mapping somewhat poorly if the ULP _may_ register memory
or just send sg_lists (like storage targets over IB/iWARP). So the ULP
will sometimes use the DMA mapping and sometimes it won't... feels
kinda off to me...
it's much saner to do:
1. dma_map_sg
2. register / send-sg-list
3. unregister (if needed)
4. dma_unmap_sg
then:
1. if register - call ib_map_mr_sg (which calls dma_map_sg)
else do dma_map_sg
2. if registered - call ib_dma_unmap_sg (which calles dma_unmap_sg)
else do dma_unmap_sg
this kinda forces ULP to completely separate these code paths with
with very little sharing.
Also, at the moment, when ULPs are doing either FRWR or FMRs
its a pain to get a non-intrusive conversion.
I'm thinking we should keep dma_map_sg out of ib_map_mr_sg, and leave
it to the ULP like it does today (at least in the first stage...)
Thoughts?
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