Paul Brook wrote: > On Sunday 30 March 2008, Anthony Liguori wrote: > > The entity processing the data shouldn't need to know or care how the > translation is done. PhysIOVector should describe everything it need to know. >
Okay, I'll update. >> What could work is if the DMA API functions mapped PhysIOVector => >> PhysIOVector and then the network and block subsystems could operate on >> a PhysIOVector. I have patches that implement vector IO for net and >> block but didn't want to include them in this series to keep things simple. >> > > IMHO this is the only sane way to implement zero-copy. > > >>>> This enables zero-copy IO to be preformed without introducing >>>> assumptions of phys_ram_base. This API is at the PCI device level to >>>> enable support of per-device IOMMU remapping. >>>> >>> By my reading it *requires* bridges be zero-copy. For big-endian targets >>> we need to ability to byteswap accesses. >>> >> You mean via ld/st_phys? >> > > By whatever means the bridge deems necessary. The whole point of the DMA API > is that you're transferring a block of data. The API allows intermediate > busses to transform that data (and address) without the block handler needing > to know or care. > > With your current scheme a byteswapping bus has to allocate a single large > buffer for the whole vector, even if the device then ends up copying unto a > local buffer in small chunks. > Oh, I see now. The DMA API should have not just a mechanism to do bulk transfers but also provide an interface to do load/store's that could potentially be byte-swapped. I didn't realize buses did that. Regards, Anthony Liguori > Paul > ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
