Real Time Issues in Live migration of Virtual Machines

1. Real Time Issues in Live migration of Virtual Machines Presented by : Ran Koretzki

2. Basic Introduction • What are VM’s ? • What is migration ? • What is Live migration ?

3. What are VM’s ? • VM’s (Virtual Machines) - "completely isolated guest operating system installation within a normal host operating system".Modern virtual machines are implemented with either software emulation or hardware virtualization or (in most cases) both together. • This allows to run multiple independent VM’s on a single physical Machine. • VM’s operating systems are not hardware depended.

4. What are VM’s ? Traditional Architecture Virtual Architecture

5. BenefitsWhat are VM’s ? • Hardware independence. • Encapsulation - VMs can be described in a file • Possible to ‘snapshot’. • Easy to move and to backup. • Easy to clone and scale wide a server application. • Many VM venders : VMware, Microsoft , Citrix… • Enables running multiple operating systems • Consolidation & use of unused computation power. • Resource management. • High availability & disaster recovery. • Easy Management. • Migration – next on the agenda.

6. Migration • Definition - The ability to move VM’s from one PH to another. • In the past, to move a VM between 2 PH, it was necessary to shutdown the VM, allocate the needed recourses to the new PH, move the VM files, and start the VM in the new host. • The recourses that need to be transferred are : memory, the internal state of the devices and of the virtual CPU. The must time consuming to transfer is memory. • The problem : downtime. The solution was at first Automation, but the real improvement came with Live Migration.

7. Live Migration • Wiki Definition - allows a server administrator to move a running virtual machine or application between different physical machines without disconnecting the client or application. For a successful live migration, the memory, storage, and network connectivity of the virtual machine needs to be migrated to the destination. • It mean it allows the server admin to move VM’s between PH transparently to the clients. • It is done usually for Load balance between PH and for migration in case of a hardware failure. • Live migration of virtual machines • Zero downtime

8. Real Time Issues in Live migration of Virtual Machines Presented by : Ran Koretzki By: Fabio Checconi, Tommaso Cucinotta, Manuel Stein.

9. Objectives of the paper • Show a heuristic to reduce the downtime of a VM during live migration by scheduling which memory pages to transmit first.

10. Assumptions , where is a memory page of size P. Available bandwidth for the transfer - b (bps). Time needed to transfer a single page - where H is the overhead Each page will be accessed for “write” with a probability of during each time frame T.

11. Algorithm At time (start of Migration)- is a set of pages to be transmitted. It is set to be the entire page set used by the VM. For do: all the pages in are transferred according to the order specified by ; The transfer ends at pages in are found dirty again; 3. Stop the VM and transfer the last pages, up to migration finishing time using a bandwidth of bps, with .

12. Crucial Values • Down Time (meaning VM not available) is - • Overall Migration time:

13. Propositions • 1. The probability of a page that is not dirty at time (start of migration) to become dirty and thus need to be transmitted in the final migration round is: • 2. The probability of a page that is dirty at time (start of migration) to become dirty and thus need to be transmitted in the final migration round is: (Where denotes the inverse of the function.)

14. The expected overall migration time (with K = 1)

15. Order of Transmission The order of transmission of the pages that minimizes the expected number of dirty pages found at the end of the live migration step must satisfy the following condition: Conclusion: If the probabilities are lower than the optimum ordering is obtained for increasing values of the probabilities On the other hand, if the probabilities are greater than the optimum ordering is obtained for decreasing values of the .

16. Reducing migration time All pages are equal, but some are more equal Problem: wasteful to transmit at each step Solution: Wait until the end, when VM is down Algorithm: among the pages that are found as dirty at start of step k, for a set of pages delay the transmission to when the VM is stopped. Which pages? (where is a threshold value) • Conclusion : It is possible to achieve a negligible increase in down-time with a substantial decrease of overall migration time.

17. A problem with this model Problem: Need to know, precisely, for each page . Solution: Gathering information during run-time. (Statistics) Problem: Non-negligible overheads. Solution: LRU - Frequency-based approach

18. Resources • Computational Resources: • Scheduling Guarantee by the Kernel – (Q, P). • Meaning period P and share Q • Network Resources: • b needs to be constant and Possible to reserve. • An unstable network is not part of this model, but a migration will still succeed (but it may not be Live Migration)

19. Simulation of the algorithm • The authors have modified the KVM hypervisor. • Page Tracing mechanism • Page accessed are traced within the hypervisor, using a bitmap • The implementation will exploit this information to modify transfer order • Simulations – • Virtualized VideoLAN Client (VLC) as a streaming server • 6500 mapped pages (16KB/page) • Transfer rate of 100MBit/sec. • 8 sec. (!)

20. Simulation of the algorithm Guaranteed bandwidth of 50 Mbit/s • Standard vs. LRU • 570 -> 300 (47%) (K=1) • 360 -> 290 (19.4%) (K=3) • 4800 -> 4500 (6.25%) (K=1) • 5500 -> 5000 (9.1%) (K=3)

21. Simulation of the algorithm LRU with delayed transmission • LRU vs. Improved LRU • 300 -> 220 (27%) (K=3) • 5000 ->4400 (12%) (K=3)

22. Conclusions • It’s possible to minimize downtime and improve QoS with simple page ordering algorithms • With a certain bandwidth, LRU has been proved as an effective aid for page ordering, achieving good results. • Further Work needs to be done…