On Thu, Mar 03, 2016 at 06:44:24PM +0800, 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. > > Performance data > ================ > > Test environment: > > CPU: Intel (R) Xeon(R) CPU ES-2699 v3 @ 2.30GHz > Host RAM: 64GB > Host Linux Kernel: 4.2.0 Host OS: CentOS 7.1 > Guest Linux Kernel: 4.5.rc6 Guest OS: CentOS 6.6 > Network: X540-AT2 with 10 Gigabit connection > Guest RAM: 8GB > > Case 1: Idle guest just boots: > ============================================ > | original | pv > ------------------------------------------- > total time(ms) | 1894 | 421 > -------------------------------------------- > transferred ram(KB) | 398017 | 353242 > ============================================ > > > Case 2: The guest has ever run some memory consuming workload, the > workload is terminated just before live migration. > ============================================ > | original | pv > ------------------------------------------- > total time(ms) | 7436 | 552 > -------------------------------------------- > transferred ram(KB) | 8146291 | 361375 > ============================================ Both cases look very artificial to me. Normally you migrate VMs which have started long ago and which can't have their services terminated before the migration, so I wouldn't expect any useful amount of free pages obtained this way. OTOH I don't see why you can't just inflate the balloon before the migration, and really optimize the amount of transferred data this way? With the recently proposed VIRTIO_BALLOON_S_AVAIL you can have a fairly good estimate of the optimal balloon size, and with the recently merged balloon deflation on OOM it's a safe thing to do without exposing the guest workloads to OOM risks. Roman. -- 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
