On 06/04/2012 05:57 PM, Isaku Yamahata wrote:
After the long time, we have v2. This is qemu part. The linux kernel part is sent separatedly. Changes v1 -> v2: - split up patches for review - buffered file refactored - many bug fixes Espcially PV drivers can work with postcopy - optimization/heuristic Patches 1 - 30: refactoring exsiting code and preparation 31 - 37: implement postcopy itself (essential part) 38 - 41: some optimization/heuristic for postcopy Intro ===== This patch series implements postcopy live migration.[1] As discussed at KVM forum 2011, dedicated character device is used for distributed shared memory between migration source and destination. Now we can discuss/benchmark/compare with precopy. I believe there are much rooms for improvement. [1] http://wiki.qemu.org/Features/PostCopyLiveMigration Usage ===== You need load umem character device on the host before starting migration. Postcopy can be used for tcg and kvm accelarator. The implementation depend on only linux umem character device. But the driver dependent code is split into a file. I tested only host page size == guest page size case, but the implementation allows host page size != guest page size case. The following options are added with this patch series. - incoming part command line options -postcopy [-postcopy-flags<flags>] where flags is for changing behavior for benchmark/debugging Currently the following flags are available 0: default 1: enable touching page request example: qemu -postcopy -incoming tcp:0:4444 -monitor stdio -machine accel=kvm - outging part options for migrate command migrate [-p [-n] [-m]] URI [<prefault forward> [<prefault backword>]] -p: indicate postcopy migration -n: disable background transferring pages: This is for benchmark/debugging -m: move background transfer of postcopy mode <prefault forward>: The number of forward pages which is sent with on-demand <prefault backward>: The number of backward pages which is sent with on-demand example: migrate -p -n tcp:<dest ip address>:4444 migrate -p -n -m tcp:<dest ip address>:4444 32 0 TODO ==== - benchmark/evaluation. Especially how async page fault affects the result.
I don't mean to beat on a dead horse, but I really don't understand the point of postcopy migration other than the fact that it's possible. It's a lot of code and a new ABI in an area where we already have too much difficulty maintaining our ABI.
Without a compelling real world case with supporting benchmarks for why we need postcopy and cannot improve precopy, I'm against merging this.
Regards, Anthony Liguori -- 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
