[openib-general] [PATCHv2] mthca: speed up memory registration by filling MTTs directly

[Michael S. Tsirkin]

> I was going to apply this, but then I realized that mthca is screwed
> up on non-cache-coherent CPUs with memfree HCAs, and this patch makes
> things much worse.  The problem is that we allocate the MTT table with
> alloc_pages() and then do pci_map_sg().  But there's no
> pci_dma_sync_sg calls when the CPU tries to write directly to the MTT
> table, and in fact not even that would work: since a
> non-cache-coherent CPU can only work on cacheline-sized chunks there's
> no safe way to touch the MTT table.
> 
> What all that means is that FMRs are currently broken for memfree on
> non-coherent CPUs.  And this patch would break all memory
> registration.  I think the fix has to be to use dma_alloc_coherent()
> to allocate the pages for the MTT table (and any other table allocated
> in lowmem -- but I don't think there are any others).
> 
> Unfortunately my PowerPC 440 system is being reworked right now so I
> can't test this for a few days.
> 
> I think this still can go into 2.6.20 after -rc1 if we can get this
> fixed up.

Just to clarify - do you plan to fix this, or are waiting for me to do it?


-- 
MST