On 05/07/2016 07:31, David Gibson wrote: > From: Alexey Kardashevskiy <a...@ozlabs.ru> > > This adds support for Dynamic DMA Windows (DDW) option defined by > the SPAPR specification which allows to have additional DMA window(s) > > The "ddw" property is enabled by default on a PHB but for compatibility > the pseries-2.6 machine and older disable it. > This also creates a single DMA window for the older machines to > maintain backward migration. > > This implements DDW for PHB with emulated and VFIO devices. The host > kernel support is required. The advertised IOMMU page sizes are 4K and > 64K; 16M pages are supported but not advertised by default, in order to > enable them, the user has to specify "pgsz" property for PHB and > enable huge pages for RAM.
Why is it not advirtised by default? When we start qemu with hugepage memory ("mount -t hugetlbfs none /mnt/kvm_hugepage" and ".. -mem-path /mnt/kvm_hugepage .."), we have an ugly message: "qemu-kvm: System page size 0x1000000 is not enabled in page_size_mask (0x11000). Performance may be slow" I understand if we want to use this with VFIO, we need something like "-global spapr-pci-host-bridge.pgsz=0x1011000". But is it needed if we don't use VFIO? Is it a way QEMU adds automatically the 0x1000000 mask to page_size_mask? Thanks, Laurent