[openib-general] [RFC/BUG] DMA vs. CQ race

[Shirley Ma]

Roland Dreier <rdreier at cisco.com> wrote on 02/27/2007 01:40:36 PM:

> Shirley, can you clarify why doing dma_alloc_coherent() in the kernel
> helps on your Cell blade?  It really seems that dma_alloc_coherent()
> just allocates some memory and then does dma_map(DMA_BIDIRECTIONAL),
> which would be exactly the same as allocating the CQ buffer in
> userspace and using ib_umem_get() to map it into the kernel.
>
> I'm looking at a possibly cleaner solution to the Altix issue, so I
> would like to make sure it fixes whatever the bug on Cell is as well.
> So any details you can provide about the problem you see on Cell would
> help a lot.
>
> Thanks...
Thanks, Roland. The failure on Cell is different with Altix issue after I
reviewed the whole thread. So this fix might not help Cell. The problem I
have might be related to multiple DMAs mapping to the same CQ. It might be
somewhere else lost the sync.

Thanks
Shirley Ma
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