Comprehensive Framework for Virtual Memory Research - Virtuoso

Virtuoso is an open-source, modular simulation framework designed for virtual memory research. The framework aims to address performance overheads caused by virtual memory by proposing solutions like improving the TLB subsystem, employing large pages, leveraging contiguity, rethinking page tables, reducing page fault latency, and employing better address mappings. Effective evaluation of virtual memory techniques is crucial and requires flexibility in modeling various schemes and considering interactions between VM components. The framework also focuses on evaluating different VM schemes based on comparison points such as TLB prefetching vs. virtual caching and transparent huge pages. Specific examples highlight the impact of VM techniques on the system, including memory allocator influence on TLB performance and main memory interference due to new page table implementations.

• Virtual Memory
• Research Framework
• Performance Optimization
• Virtual Memory Solutions
• Evaluation Techniques

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1. Virtuoso An Open-Source, Comprehensive and Modular Simulation Framework for Virtual Memory Research https://github.com/CMU-SAFARI/Virtuoso Konstantinos Kanellopoulos Konstantinos Sgouras Onur Mutlu

2. Improving Virtual Memory Virtual memory causes high performance overheads Various academic and industrial solutions were proposed to reduce these overheads 2

3. Virtual Memory (VM) Solutions Improving the TLB Subsystem Employing Large Pages Leveraging Contiguity Rethinking Page Tables Reducing Page Fault Latency Employing Better Address Mappings 3

4. Evaluating VM Solutions Effectively evaluating VM techniques is crucial for progress in the domain 4

5. Evaluation Requirements Flexibility to model many VM schemes Interactions between VM components Impact of VM techniques on system 5

6. Evaluation Requirements Flexibility to model many VM schemes 6

7. Evaluating Various VM Schemes Set of comparison points New idea on VM TLB Prefetching vs. Virtual Caching Transparent Huge Pages 7

8. Evaluation Requirements Interactions between VM components 8

9. Example: TLB and Memory Allocator Memory Allocator TLB TLB performance heavily depends on the memory allocator (e.g., # of 2MB pages) 9

10. Evaluation Requirements Impact of VM techniques on system 10

11. Example: Main Memory Interference New Page Table Low Latency High Interference 11

12. Lack of Comprehensive Simulators Ramulator gem5 ZSim Sniper ChampSim Modern simulators lack the capability to model a wide range of state-of-the-art VM techniques 12

13. Our Approach: Virtuoso Virtuoso TLBs Page Table Protection Metadata Memory Allocator Memory Subsystem Out-of-Order Core Interconnects Example: Sniper Multicore Simulator1 [1] Carlson et al. An Evaluation of High-Level Mechanistic Core Models TACO 2014 13

14. Virtuoso: Key Benefits Comprehensive Modular Open-Source https://github.com/CMU-SAFARI/Virtuoso 14

15. Virtuoso: Key Benefits Comprehensive 15

16. Virtuoso: Tool Set 6 TLB Schemes 4 Page Table Designs MMU Nesting for Virtualized Environments Intermediate Address Space Schemes 2 Metadata Schemes for Protection 2 Contiguity- aware Schemes https://github.com/CMU-SAFARI/Virtuoso 16

17. VirtuOS: Mini-OS for Memory Management What about the OS? Challenge: We need to both simulate and emulate it 17

18. VirtuOS: Mini-OS for Memory Management Example Routine: Page Fault Handler Functional Events Allocate Page Microarchitectural Events addi load Promote Page Virtuoso Emulate Simulate 18

19. Virtuoso: Key Benefits Modular 19

20. Virtuoso: Modularity Virtuoso Virtuoso Virtuoso Sniper ZSim gem5 20

21. Virtuoso: Key Benefits Open-Source https://github.com/CMU-SAFARI/Virtuoso 21

22. Virtuoso is Open Source https://github.com/CMU-SAFARI/Virtuoso 22

23. Virtuoso Example Use Cases Comparing MMU Designs Effect of THP on PTW Latency 23

24. Virtuoso Example Use Cases Comparing MMU Designs Effect of THP on PTW Latency 24

25. Comparing MMU Designs 1.2 Speedup over Radix 1.1 1.0 0.9 Effective comparison of different MMU designs 25

26. Virtuoso Example Use Cases Comparing MMU Designs Effect of THP on PTW Latency 26

27. Interplay between PTW and THP 1.2 PTW Performance 1.0 0.8 0.6 0.4 0.2 0.0 0 1 2 3 4 5 6 7 8 9 10 Low Fragmentation -> High Fragmentation Effective evaluation of THP & PTW interactions 27

28. Conclusion Virtuoso TLBs Page Table Contiguity Techniques Protection Metadata VirtuOS Virtuoso is a good start for establishing a common ground for VM research https://github.com/CMU-SAFARI/Virtuoso

29. Virtuoso An Open-Source, Comprehensive and Modular Simulation Framework for Virtual Memory Research https://github.com/CMU-SAFARI/Virtuoso Konstantinos Kanellopoulos Konstantinos Sgouras Onur Mutlu