VTd is the 'virtualised device' acceleration within the CPU - it has been very problematic with the igfx so far, but supposedly Ivybridge works. intel_iommu=off disables support and thus allows the GPU to have direct access to memory without going through a DMA remapper.
VTd is the 'virtualised device' acceleration within the CPU - it has been very problematic with the igfx so far, but supposedly Ivybridge works. intel_iommu=off disables support and thus allows the GPU to have direct access to memory without going through a DMA remapper.