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| -rw-r--r-- | docs/all/index.rst | 2 | ||||
| -rw-r--r-- | docs/all/live_migration.rst | 108 | ||||
| -rw-r--r-- | docs/all/lmdowntime.jpg | bin | 0 -> 6372 bytes | |||
| -rw-r--r-- | docs/all/lmnetwork.jpg | bin | 0 -> 53332 bytes | |||
| -rw-r--r-- | docs/all/lmtotaltime.jpg | bin | 0 -> 24171 bytes |
5 files changed, 109 insertions, 1 deletions
diff --git a/docs/all/index.rst b/docs/all/index.rst index fed745ee6..6de846da1 100644 --- a/docs/all/index.rst +++ b/docs/all/index.rst @@ -41,4 +41,4 @@ Setup Guides environment-setup tunning - + live_migration diff --git a/docs/all/live_migration.rst b/docs/all/live_migration.rst new file mode 100644 index 000000000..51265cc8d --- /dev/null +++ b/docs/all/live_migration.rst @@ -0,0 +1,108 @@ +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. Testingt 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: +:: + /root/qemu.git/x86_64-softmmu/qemu-system-x86_64-enable-kvm -cpu host -smp 4 –device virtio-net-pci,netdev=net1,mac=52:54:00:12:34:56 –netdev type=tap,id=net1,script=/etc/kvm/qemu-ifup,downscript=no,vhost=on–device virtio-net-pci,netdev=net2,mac=54:54:00:12:34:56 –netdevtype=tap,id=net2,script=/etc/kvm/qemu-ifup2,downscript=no,vhost=on -balloon virtio -m 8192-monitor stdio /mnt/liang/ia32e_rhel6u5.qcow + +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% diff --git a/docs/all/lmdowntime.jpg b/docs/all/lmdowntime.jpg Binary files differnew file mode 100644 index 000000000..c9faa4c73 --- /dev/null +++ b/docs/all/lmdowntime.jpg diff --git a/docs/all/lmnetwork.jpg b/docs/all/lmnetwork.jpg Binary files differnew file mode 100644 index 000000000..8a9a324c3 --- /dev/null +++ b/docs/all/lmnetwork.jpg diff --git a/docs/all/lmtotaltime.jpg b/docs/all/lmtotaltime.jpg Binary files differnew file mode 100644 index 000000000..2dced3987 --- /dev/null +++ b/docs/all/lmtotaltime.jpg |
