The Hybrid Scheduling
Framework for Virtual Machine
Systems
Authors
• 翁楚良，男，博士，副教授。
• 2001年进入上海交通大学计算机系学习，从事并
行与分布计算、集群计算与网格计算等研究工作。
2004年博士毕业留校工作。
• 研究兴趣涉及虚拟化技术、并行与分布计算、网
格计算与集群计算、高性能计算、系统安全等。
同时负责网格计算中心的 IBM P690 、 IBM
e1350 集群、 Intel Itanium2 服务器等高性能计算
机的系统管理和相关开发工作。
This team’s work
• Automatic Performance Tuning for the
Virtualized Cluster System ---- ICDCS2009
The Problem
• The scheduling strategy in Xen
(Asynchronous CPU scheduling strategy)
may deteriorate the performance when the
virtual machine is used to execute the
concurrent applications such as parallel
programs or multithreaded programs.
Why?
• All virtual CPUs in a SMP virtual machine
are usually not online all the time, and
possibly not online at the same time(多线
程程序需要相关所有CPU当前online才能继
续运行), so the scheduling methods may
deteriorate the performance.
Why?
VM
VM
Guest
App.
vCPU
Physical
Hardware
Guest
App.
vCPU
vCPU
?
pCPU
pCPU
Why?
• In the worst case, all the VMs are
suspended even in the condition of
enough physical CPUs.
Just imagine 4 VMs have 2 vCPUs
each on a 4-core platform.
Solution
•
Recognize two types of virtual machines
in the system:
– the high-throughput type -- default
– the concurrent type -- when the majority of
its workload is concurrent applications
Solution
•
•
When it is a concurrent VM, its virtual
CPUs are mapped into physical CPUs
synchronously ---- VM granularity
schedule (Coscheduling)
Otherwise its virtual CPUs are mapped
asynchronously. ---- vCPU granularity
schedule
Hybrid Schedule Framework
Design Key Notes
•
To maximize the performance in the virtual
machine system, the following design issues
should be considered for the scheduler in the
VMM.
–
–
–
–
Fairness
Workload Balancing
Wasted CPU Time
Adaptiveness
Xen Scheduler
•
Three scheduling algorithms in Xen:
– Borrowed Virtual Time (BVT)
– Simple Earliest Deadline First (SEDF)
– Credit Scheduling
Borrowed Virtual Time (BVT)
•
•
•
•
•
Fair-share scheduling algorithm
Schedule the runnable VM with the
smallest virtual time firstly
The client can effectively borrow virtual
time from its future CPU allocation.
Low latency support ---- for realtime and
interactive applications
Shortage : lack of the non work conserving (NWC) mode
Simple Earliest Deadline First
(SEDF)
•
•
•
The real time property is used to ensure
time guarantees
a VM will receive at least the slice
specified by the VM in each period of the
length specified by the VM.
Can indicate whether the VM is eligible
to receive extra CPU time (workconserving mode).
Simple Earliest Deadline First
(SEDF)
•
•
•
Shortage:
Lack of global workload balancing on
multiprocessors
The CPU fairness depends on the value
of the period.
Credit Scheduling
•
•
•
•
One of proportional share (PS) strategies
Automatic workload balancing
This algorithm can efficiently achieve a
global workload balancing on a SMP
system when the majority of the
workload is not the high concurrent
application.
Default scheduling algorithm in Xen