On Tue, Dec 11, 2012 at 3:13 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > On Mon, Dec 10, 2012 at 02:09:36PM +0100, Stefan Hajnoczi wrote: >> The data plane thread needs to map guest physical addresses to host >> pointers. Normally this is done with cpu_physical_memory_map() but the >> function assumes the global mutex is held. The data plane thread does >> not touch the global mutex and therefore needs a thread-safe memory >> mapping mechanism. >> >> Hostmem registers a MemoryListener similar to how vhost collects and >> pushes memory region information into the kernel. There is a >> fine-grained lock on the regions list which is held during lookup and >> when installing a new regions list. > > Can we export and reuse the vhost code for this? > I think you will find this advantageous when you add migration > support down the line. > And if you find it necessary to use MemoryListener e.g. for performance > reasons, then vhost will likely benefit too.
It's technically possible and not hard to do but it prevents integrating deeper with core QEMU as the memory API becomes thread-safe. There are two ways to implement dirty logging: 1. The vhost log approach which syncs dirty information periodically. 2. A cheap thread-safe way to mark dirty outside the global mutex, i.e. a thread-safe memory_region_set_dirty(). If we can get thread-safe guest memory load/store in QEMU then #2 is included. We can switch to using hw/virtio.c instead of hw/dataplane/vring.c, we get dirty logging for free, we can drop hostmem.c completely, etc. Stefan
