Virtual Machine Scheduling for Parallel Soft Real-Time Applications

Virtual Machine Scheduling for Parallel Soft Real-Time Applications

Like Zhou, Song Wu, Huahua Sun, Hai Jin, Xuanhua Shi

Services Computing Technology and System LabCluster and Grid Computing Lab

School of Computer Science and TechnologyHuazhong University of Science and Technology

Outline

• Introduction• Motivation• Design• Implementation• Evaluation• Discussion and Future Work• Conclusion

Introduction• Many soft real-time applications use parallel

programming models to utilize hardware resources better and possibly shorten response time

• More and more cloud services including such parallel soft real-time applications (PSRT applications) are running in virtualized environment

cloud-based live transcoding computer visiondistributed real-time

stream computing

Introduction• When running in virtualized environment, PSRT

applications do not behave well and only obtain inadequate performance

Outline


Motivation

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soft real-time scheduling

co-scheduling

parallel soft real-time scheduling

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How to design and implement the parallel soft real-time scheduling algorithm which addresses soft real-time constraints and synchronization problems simultaneously?

Outline


Overall Design

Address Soft Real-Time Constraints

• How to handle soft real-time constraints of event-driven soft real-time applications?

PCPU0

PCPU0 VCPU0VCPU0 RT-

VCPU0RT-

VCPU0 VCPU1VCPU1 VCPU2VCPU2 VCPU3VCPU3

receive external events

PCPU0

PCPU0

RT-VCPU0

RT-VCPU0 VCPU0VCPU0 VCPU1VCPU1 VCPU2VCPU2 VCPU3VCPU3

descheduled

PCPU0

PCPU0 VCPU0VCPU0 VCPU1VCPU1 RT-

VCPU0RT-

VCPU0 VCPU2VCPU2 VCPU3VCPU3

real-time boost under over


• How to handle soft real-time constraints of time-driven soft real-time applications?

VCPU0VCPU0 VCPU1VCPU1 VCPU2VCPU2 RT-VCPU0RT-VCPU0 VCPU0VCPU0 VCPU1VCPU1 VCPU2VCPU2

VCPU0

VCPU0

VCPU1

VCPU1

VCPU2

VCPU2

RT-VCPU0

RT-VCPU0

VCPU0

VCPU0

VCPU0

VCPU0

VCPU0

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VCPU0

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VCPU1

VCPU1

VCPU1

VCPU1

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VCPU1

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VCPU2

VCPU2

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VCPU2

VCPU2

RT-VCPU0

RT-VCPU0

RT-VCPU0

RT-VCPU0

RT-VCPU0

RT-VCPU0

has RT-VMs no RT-VMs


• How to calculate time slice?S the length of time slice the scheduler used

LTS long time slice

NR the total number of RT-VCPUs in the system

NV the number of VCPUs per PCPU

L the expected latency of soft real-time applications

WCSL worst case scheduling latency

Calculate WCSL:

L and WCSL must meet:

Calculate S:


• How to determine the approximate value of the expected latency?– We use the VoIP test of MyConnection Server (MCS) to

conduct an experiment

– The time slice with the value of 5ms is good enough to guarantee the quality of VoIP while minimizing the impact on other applications

– The value of L is calculated as 15ms

Time slice Upstream jitter

Upstream packet loss

Packet discards

MOS

30ms 7.8ms 9.5% 3.0% 1.0

15ms 6.7ms 7.2% 0.9% 1.0

5ms 5.0ms 0.1% 0% 4.0

3ms 4.8ms 0% 0% 4.0

Solve Synchronization Problems

• How to handle synchronization problems?

PCPU1

PCPU1 VCPU1VCPU1 VCPU2VCPU2 VCPU0VCPU0

PCPU0

PCPU0

RT-VCPU0


PCPU2

PCPU2

RT-VCPU2

RT-VCPU2 VCPU1VCPU1 VCPU0VCPU0 VCPU3VCPU3

PCPU3

PCPU3

RT-VCPU1

RT-VCPU1 VCPU2VCPU2 VCPU3VCPU3


RT-VCPU3

RT-VCPU3VCPU3VCPU3

VCPU2VCPU2

VCPU0VCPU0VCPU1VCPU1

soft interrupt

• How to address the VCPU migration problem?

Solve Synchronization Problems

PCPU0

PCPU0 VCPU0VCPU0 RT-

VCPU0RT-

VCPU0 VCPU1VCPU1 VCPU2VCPU2 VCPU3VCPU3


PCPU1

PCPU1

RT-VCPU1


steal

RT-VM

VCPU migration problem

affinity exchange RT-VCPU0

RT-VCPU0

0 1 0 1CPU affinity

RT-VCPU1

RT-VCPU1

1 0 1 0CPU affinity

Parallel Soft Real-Time Scheduling

Calculate time slice

Schedule all runnable VCPUs of a RT-VM

Outline


Implementation• Poris: parallel soft real-time scheduler

– User interface:• add a field named type to csched_dom• add a field named latency to csched_dom• add a new command xm sched-rt

– Modification to the Credit scheduler (sched_poris):• add a new priority (CSCHED _PRI _TS _RT) as the real-

time priority• modify event processing• modify the VCPU and PCPU operating functions• manage CPU affinity and modify csched_schedule() to

co-schedule all runnable VCPUs of a RT-VM

Outline


Experiment Setup• Hardware and VM configuration

• Software– Hypervisor: Xen-4.0.1– OS: CentOS 5.5 distribution with the Linux-2.6.31.8 kernel

• Interfering configuration– CPU-intensive interfering configuration: all interfering VMs run CPU-intensive

workloads– mixed interfering configuration: some interfering VMs run CPU-intensive

workloads, and some run I/O-intensive workloads

Name Hardware configuration VM configuration

Machine I a dual-core 2.6GHz Intel CPU, 2GB memory, 500GB SATA disk and 100Mbps Ethernet card

2VCPUs, 256MB memory and 10GB virtual disk

Machine II two quad-core 2.4GHz Intel Xeon CPUs, 24GB memory, 1TB SCSI disk and 1Gbps Ethernet card

8VCPUs, 1GB memory and 10GB virtual disk

Experiments• Does Poris guarantee the QoS of VoIP applications?

– Experiments with MyConnection Server

• Is Poris suitable for client-side virtualization?– Experiments with Media Player

• Does Poris surpass other schedulers?– Experiments with PARSEC Benchmark

• What is the impact of Poris on non-real-time workloads?– Experiments with Non-real-time Workloads (Kernel

compilation, Postmark, Stream benchmark)

• Upstream jitter

MyConnection Server

(a) CPU-intensive interfering configuration

(b) Mixed interfering configuration

MyConnection Server• VoIP test results

Interfering configuration

Scheduler Upstream jitter

Downstream jitter

Packet discards

MOS

CPU-intensive Credit 11.9ms 9.6ms 4.4% 1.0

Poris 4.6ms 1.2ms 0.0% 4.0

Mixed Credit 10.4ms 6.5ms 2.0% 1.0

Poris 4.5ms 0.6ms 0.0% 4.0

61.34% ↓ 87.5% ↓

56.73% ↓ 90.77% ↓

Media Player• Play low resolution video



71.19% ↑

40.68% ↑

Media Player• Play high resolution video



135.94% ↑

95.31% ↑

PARSEC Benchmark

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CreditRSPSPoris

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CreditRSPSPoris

The performance of Poris is up to 44.12% better than

Credit, 41.28% better than RS, and 28.02% better than

PS.

Non-real-time workloads

Kernel compilation Postmark

Stream benchmark

Because Poris promotes the priorities of RT-VCPUs temporarily and uses dynamic time slices, the interferences of Poris on non-real-time workloads are slight and acceptable.

Poris even increases the performance of some types of non-real-time workloads, such as I/O-intensive workloads.

Outline


Discussion and Future Work• Determining VM type and expected latency

– provide APIs to programmers– analyze runtime characteristics of applications

• Many applications running in a VM– use previous techniques to identify real-time applications

• Supporting multiple VMs running the same PSRT applications– co-schedule multiple VMs by analyzing the communication

patterns of VMs running the same PSRT applications

Outline


Conclusion• We identify the scheduling problems in virtualized

environment, and find existing CPU scheduling mechanisms do not fit for PSRT applications

• We propose a novel parallel soft real-time scheduling algorithm

• We implement a prototype in the Xen hypervisor based on the algorithm, named Poris

• We verify the effectiveness of Poris through various applications. The experimental results show that Poris can improve the performance of PSRT applications significantly

Thank you！

System Virtualization

Hypervisor

Hardware

VM

Applications

Guest OS

VM

Applications

Guest OS

Credit Scheduler• CPU resources (or credits) are distributed to VCPUs of

VMs in proportion to their weight

• three kinds of VCPU priorities: boost, under, and over

• VCPUs with the same priority are scheduled in FCFS manner

• supports SMP platforms well

Documents

Virtual Machine Scheduling for Parallel Soft Real-Time Applications