On (Thu) 03 Mar 2016 [18:44:24], Liang Li wrote: > The current QEMU live migration implementation mark the all the > guest's RAM pages as dirtied in the ram bulk stage, all these pages > will be processed and that takes quit a lot of CPU cycles. > > From guest's point of view, it doesn't care about the content in free > pages. We can make use of this fact and skip processing the free > pages in the ram bulk stage, it can save a lot CPU cycles and reduce > the network traffic significantly while speed up the live migration > process obviously. > > This patch set is the QEMU side implementation. > > The virtio-balloon is extended so that QEMU can get the free pages > information from the guest through virtio. > > After getting the free pages information (a bitmap), QEMU can use it > to filter out the guest's free pages in the ram bulk stage. This make > the live migration process much more efficient. > > This RFC version doesn't take the post-copy and RDMA into > consideration, maybe both of them can benefit from this PV solution > by with some extra modifications. I like the idea, just have to prove (review) and test it a lot to ensure we don't end up skipping pages that matter. However, there are a couple of points: In my opinion, the information that's exchanged between the guest and the host should be exchanged over a virtio-serial channel rather than virtio-balloon. First, there's nothing related to the balloon here. It just happens to be memory info. Second, I would never enable balloon in a guest that I want to be performance-sensitive. So even if you add this as part of balloon, you'll find no one is using this solution. Secondly, I suggest virtio-serial, because it's meant exactly to exchange free-flowing information between a host and a guest, and you don't need to extend any part of the protocol for it (hence no changes necessary to the spec). You can see how spice, vnc, etc., use virtio-serial to exchange data. Amit -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
