Messages in this thread |  | | | Date | Tue, 15 Jul 2008 20:10:42 -0700 (PDT) | | Subject | Re: [SUGGESTION]: drop virtual merge accounting in I/O requests | | From | David Miller <> |
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From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Date: Tue, 15 Jul 2008 02:45:03 +0900
> dma_4u_map_sg() has: > > if (segstart != s) { > /* We cannot merge if: > * - allocated dma_addr isn't contiguous to previous allocation > */ > if ((dma_addr != dma_next) || > (outs->dma_length + s->length > max_seg_size) || > (is_span_boundary(out_entry, base_shift, > /* Can't merge: create a new segment */ > segstart = s; > outcount++; > outs = sg_next(outs); > > So if the IOMMU allocated dma_addr isn't contiguous to previous > allocation, it might not merge segments that the block layer expected > the IOMMU to merge. > > We need kinda two phase merging code such as the old SPARC64 IOMMU > code and PARISC IOMMUs though I like the new simple SPARC64 IOMMU > code.
I see.
I wonder if all that complexity is really worth it. Also, all of this IOMMU allocation and mapping code runs under a spinlock with hw IRQs disabled.
More and more I'm seeing that it's likely better to remove the VMERGE code. I can't see what it really buys us anymore, and to make it work requires quite a large amount of complexity in the IOMMU layer.
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