Optimizing Virtual Machines Using Hybrid Virtualization

Qian LinShanghai Jiao Tong University

SAC 2011 -- OS track

Agenda

Background: system virtualization

Motivation

Design and optimization

Evaluation

Summary

Background: system virtualization

Goal: consolidate and maximize H/W platform resources

Way: multiple VMs run concurrently on a single machine

Motivation

Current virtualization types

Software-only full virtualization Dynamic binary translation technique For cross-platform development and debug only

H/W assisted full virtualization Leverage H/W virtualization extension of CPU architecture Superior in CPU and memory virtualization, but not in I/O

Paravirtualization Ring compression → compromised strategy Exist much overhead in the execution of system call Efficient in I/O event handling

Motivation (cont.)

Reduce overhead incurred by virtualization

Optimize to reduce the execution redundancy

Hybrid approach to merge advantages

64-bit HVM is at par or faster than 64-bit PVM

Paravirtualization is helpful for enhancing HVM Simplicity, performance, efficiency, scalability, correctness

Design

Type I: Hybrid PVM

Port paravirtualized OS

into HVM container

Add HAP support

Type II: Hybrid HVM

Local optimize HVM

using PV strategy

Import PV components

Common design goal: Run paravirtualized OS in the HVM container.

VM optimization (1)

Abridge the system call path

PVM: Kernel/User space share the same ring

Hybrid VM: Rings are assigned normally

VM optimization (2)

Shadow page table → complex and dull

VM optimization (2)

H/W assisted paging → accelerated!

VM optimization (3)

Local APIC is not used by Hybrid VM Linux

EOI (End of Interrupt) does not cause VM exit.

Use Xen API (event channel)

MSI/MSI-X handling is paravirtualized in Hybrid VM

MSI Mask/Unmask does not cause VM exit

No changes are made to device drivers

I/O intensive loads expose those virtualization overheads

About 12K interrupts/per sec. (per VCPU) with 10 GbE

CPU utilization is >3% higher per VCPU on ordinary HVM

Linux

As number of VCPUs increases, overhead increases

Micro performance (1)

LMBench - Processor

Overhead contributed by fundamental

operations

Factor: system call

Micro performance (2)

LMBench - Context switch

Inter processes, kernel/user mode, interrupt

Factor: address translation, TLB flush

Micro performance (3)

LMBench - Local communication latency

Response time of I/O request

Factor: address translation

Macro performance: CPU intensive

Kernel compile benchmark

Factor: system call, context switch, address translation

Macro performance: I/O intensive

CPU utilization within Ethernet workload

Factor: interrupt handling

Summary

Minimize virtualization overheads and utilize new/advanced H/W features in VMs as much as possible for cloud computing

Take both superiority of H/W assisted virtualization and paravirtualization

Open source implementation of prototype

Also release to the Xen community

Thank you!

Trusted Computing Group @ SJTU

http://202.120.40.124/index.php/Project_TC