+++ /dev/null
-.. This work is licensed under a Creative Commons Attribution 4.0 International License.
-.. http://creativecommons.org/licenses/by/4.0
-.. (c) <optionally add copywriters name>
-
-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%
Code Review / kvmfornfv.git / blobdiff