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diff --git a/docs/userguide/live_migration.userguide.rst b/docs/userguide/live_migration.userguide.rst deleted file mode 100644 index 9fa9b82fd..000000000 --- a/docs/userguide/live_migration.userguide.rst +++ /dev/null @@ -1,121 +0,0 @@ -.. This work is licensed under a Creative Commons Attribution 4.0 International License. - -.. http://creativecommons.org/licenses/by/4.0 - -Fast Live Migration -=================== - -The NFV project requires fast live migration. The specific requirement is -total live migration time < 2Sec, while keeping the VM down time < 10ms when -running DPDK L2 forwarding workload. - -We measured the baseline data of migrating an idle 8GiB guest running a DPDK L2 -forwarding work load and observed that the total live migration time was 2271ms -while the VM downtime was 26ms. Both of these two indicators failed to satisfy -the requirements. - -Current Challenges ------------------- - -The following 4 features have been developed over the years to make the live -migration process faster. - -+ XBZRLE: - Helps to reduce the network traffic by just sending the - compressed data. -+ RDMA: - Uses a specific NIC to increase the efficiency of data - transmission. -+ Multi thread compression: - Compresses the data before transmission. -+ Auto convergence: - Reduces the data rate of dirty pages. - -Tests show none of the above features can satisfy the requirement of NFV. -XBZRLE and Multi thread compression do the compression entirely in software and -they are not fast enough in a 10Gbps network environment. RDMA is not flexible -because it has to transport all the guest memory to the destination without zero -page optimization. Auto convergence is not appropriate for NFV because it will -impact guest’s performance. - -So we need to find other ways for optimization. - -Optimizations -------------------------- -a. Delay non-emergency operations - By profiling, it was discovered that some of the cleanup operations during - the stop and copy stage are the main reason for the long VM down time. The - cleanup operation includes stopping the dirty page logging, which is a time - consuming operation. By deferring these operations until the data transmission - is completed the VM down time is reduced to about 5-7ms. -b. Optimize zero page checking - Currently QEMU uses the SSE2 instruction to optimize the zero pages - checking. The SSE2 instruction can process 16 bytes per instruction. - By using the AVX2 instruction, we can process 32 bytes per instruction. - Testing shows that using AVX2 can speed up the zero pages checking process - by about 25%. -c. Remove unnecessary context synchronization. - The CPU context was being synchronized twice during live migration. Removing - this unnecessary synchronization shortened the VM downtime by about 100us. - -Test Environment ----------------- - -The source and destination host have the same hardware and OS: -:: -Host: HSW-EP -CPU: Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz -RAM: 64G -OS: RHEL 7.1 -Kernel: 4.2 -QEMU v2.4.0 - -Ethernet controller: Intel Corporation Ethernet Controller 10-Gigabit -X540-AT2 (rev 01) -QEMU parameters: -:: -${qemu} -smp ${guest_cpus} -monitor unix:${qmp_sock},server,nowait -daemonize \ --cpu host,migratable=off,+invtsc,+tsc-deadline,pmu=off \ --realtime mlock=on -mem-prealloc -enable-kvm -m 1G \ --mem-path /mnt/hugetlbfs-1g \ --drive file=/root/minimal-centos1.qcow2,cache=none,aio=threads \ --netdev user,id=guest0,hostfwd=tcp:5555-:22 \ --device virtio-net-pci,netdev=guest0 \ --nographic -serial /dev/null -parallel /dev/null - -Network connection - -.. figure:: lmnetwork.jpg - :align: center - :alt: live migration network connection - :figwidth: 80% - - -Test Result ------------ -The down time is set to 10ms when doing the test. We use pktgen to send the -packages to guest, the package size is 64 bytes, and the line rate is 2013 -Mbps. - -a. Total live migration time - - The total live migration time before and after optimization is shown in the - chart below. For an idle guest, we can reduce the total live migration time - from 2070ms to 401ms. For a guest running the DPDK L2 forwarding workload, - the total live migration time is reduced from 2271ms to 654ms. - -.. figure:: lmtotaltime.jpg - :align: center - :alt: total live migration time - -b. VM downtime - - The VM down time before and after optimization is shown in the chart below. - For an idle guest, we can reduce the VM down time from 29ms to 9ms. For a guest - running the DPDK L2 forwarding workload, the VM down time is reduced from 26ms to - 5ms. - -.. figure:: lmdowntime.jpg - :align: center - :alt: vm downtime - :figwidth: 80% |