On Mon, 2011-01-24 at 14:36 -0500, David Dillow wrote: > On Mon, 2011-01-24 at 10:18 -0500, Or Gerlitz wrote: > > I see, thanks for clarifying this out load and clear, so maybe you'll > > first get the seven srp patches reviewed and merged, and only then see > > if/what benefit this patch brings, I'm a little bit worried of > > changing something below everyone's (srp, iser, rds, p9, nfs-rdma, > > lustre, etc) legs which doesn't have any notable benefit, I would be > > happy to hear others/opinions > > Well, I believe it only affects the block merging -- I have to catch a > flight, so I cannot recheck right this moment -- that limits the effects > to SRP and iSER. The others don't use it at all.
Ok, finally got a chance to look into this a bit further. The block layer is the only direct user of it, though a few IOMMU drivers reference it as well for their *_map_sg coalescing code. pci-gart_64 on x86, and a smattering on on sparc, powerpc, and ia64. Since other IB protocols could potentially see larger segments with this, let's check those: iSER is fine, because you limit your maximum request size to 512 KB, so we'll never overrun the page vector in struct iser_page_vec (128 entries currently). It is independent of the DMA segment size, and handles multi-page segments already. IPoIB is fine, as it maps each page individually, and doesn't use ib_dma_map_sg(). RDS appears to do the right thing and has no dependencies on DMA segment size, but I don't claim to have done a complete audit. NFSoRDMA and 9p are OK -- they do not use ib_dma_map_sg(), so they doesn't care about the coalescing. Lustre's ko2iblnd does not care about coalescing -- it properly walks the returned sg list. I don't see anything that would have a problem with larger DMA segment sizes; some of them would see small efficiency gains similar to SRP if more small segments could be coalesced into fewer larger ones. -- Dave Dillow National Center for Computational Science Oak Ridge National Laboratory (865) 241-6602 office -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
