cloud operating system unit 09 cloud os core technology m. c. chiang department of computer science...

Cloud Operating System

Unit 09Cloud OS Core

Technology M. C. Chiang

Department of Computer Science and Engineering National Sun Yat-sen University

Kaohsiung, Taiwan, ROC

Cloud Operating System

Outline

Main Characteristics of Cloud Computing Why Virtualization? Hardware Virtualization

Full virtualization Paravirtualiztion Hardware-assisted virtualization

Device Driver Virtualization Memory Virtualization

Local vs. Distributed

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Main Characteristics of Cloud Computing On-demand self-service Broad network access Resource pooling Rapid elasticity Measured service


Main Characteristics of Cloud Computing On-demand self-service

System demands resource automatically

Broad network access Resource pooling

Virtualizing resources such as memory, storage, CPU into pools.

Rapid elasticity Provisioning or releasing resources at anytime

Measured service


History of Virtualization (1) 1964 – IBM CP-40. 1965 – IBM System/360-67, with virtual memory hardware. 1999 – Full Virtualization. VMware. 2003 – Para-Virtualization. Xen. 2005 – HW-Assisted Virtualization. Intel VT-x, AMD-V. 2006 – QEMU. 2007 – KVM (Kernel-based Virtual Machine). Linux 2.6.20.


History of Virtualization (2)

From another perspective, the development of virtualization can be divided into the following stages: Mainframe Virtualization Desktop Virtualization Server Virtualization Cloud Computing Nowadays. Mobile Virtualization On the way.


History of Virtualization (3)

The reasons of x86 virtualization: Low infrastructure utilization. Increasing physical infrastructure costs. Increasing IT management costs. Insufficient failover and disaster protection. High maintenance end-user desktop. x86 is widespread.


Applying Virtualization to Cloud With virtualizing resources, they can easily be

put into pools. Virtualized CPU and memories can be

distributed dynamically to virtual machines in real time. Leads to Rapid elasticity and On-demand self-

service

Imagine ‘hot plug memories/CPU’ into machines.


Hardware Virtualization (1)

How to realize x86 virtualization? What’s the problem encountered? How to deal with the problem?



112/04/20 Cloud Operating System - Uint 09: Core Technique

Traditionally, OS is at Ring 0 for

hardware resource

management. When realizing

virtualization, VMM

is at Ring 0, and

OS is downgraded

to Ring 1.

U01-11


According to Popek and Goldberg, CPU instructions can be classified into three sets. Privileged instructions. Sensitive instructions. Critical instructions.

*1: GJ Popek and RP Goldberg, “Formal

requirements for virtualizable third

generation architectures”, Communication

of the ACM, vol 17, pp. 412-421, July,

1974.



Instruction which will modify the configuration of resources should either be executed in Ring 0 (privileged mode) or trap.

There are 17 instructions in x86 architecture may cause problem. Why? They are unprivileged.

Won’t cause trap when execution.

They expose physical processor state. Reveal some details which shouldn’t be.



There are three approaches for virtualization available nowadays. Full Virtualization. ParaVirtualization. Hardware-Assisted Virtualization.


Full Virtualization Binary Translation.

Replace nonvirtualizable instructions with new sequences of instructions which have the same effect as original on the virtual hardware.

Many instructions replace one, so if the instruction is frequently used, the overhead is huge.

Huge cost on resources. Better compatibility. VMware, QEMU.112/04/20 Cloud Operating System - Uint 09: Core Technique U01-17

ParaVirtualization (1)

Also named OS-assisted virtualization. OS kernel adaptation. Performing corresponding hypercalls instead of

the original privileged instructions. Low cost of CPU and I/O. Compatibility worse than Full Virtualization. Meet problems when the kernel is not open. Citrix Xenserver, Microsoft hyper-V.


ParaVirtualization (2)

Hypercall is quite similar to system call. Implementation of Xen.

System call: an interrupt (0x80) from user space to kernel space.

Hypercall: an interrupt (0x82) from guest domain (Ring 1) to hypervisor (Ring 0).

Both system call table and hypercall table are defined in file “arch/x86/kernel/entry_64.S”.


Hardware-Assisted Virtualization (1) Re-design the hardware architecture. Add new instruction sets for x86 architecture to

trap those nonvirtualizable instructions. Conceptually, hypervisor stays at “Ring -1”. No need to de-privilege the guest OS. AMD AMD-V, Intel VT-x.


Hardware-Assisted Virtualization (2) Intel VT-x:

First supported by Pentium 4 (Model 662 and 672) on 2005.

Two operating mode: VMX Root Operation (for VMM). Non-Root Operation (for Guest OS).

Extented Page Tables.


Hardware-Assisted Virtualization (3) AMD AMD-V:

On 2006, first supported by Athlon 64, Athlon 64 X2 and Athlon 64 FX.

Two modes for hypervisor to handle memory partitioning: Shadow Page Tables. Nested Page Tables.


Device Driver Virtualization – the Idea Virtual machines need their own device drivers.

For guest OSs to communicate with physical hardware.

Most virtualization solutions emulated simple devices that the drivers already existed. Like IDE interface and NE2000 (a very old nic).


Device Driver Virtualization – in Practice Xen Hypervisor’s

paravirtulization solution: Requests from front-end

drivers in DomU writes into a ring-buffer shared with Dom0.

Dom0 handles the request by the back-end drivers in kernel, and access the hardware by real drivers.

Then back-end write response back and consumed by guest.


Device Driver Virtualization

The Split Driver


Memory Virtualization

Modern Operating system and x86 hardware mostly support memory virtualization. In user-space applications access to virtual memory

with paging mechanism. VM instance hosts with a OS support virtual memory

means an addition layers of memory mapping. Newer CPUs have optimizations for addition layers

of mapping. Additional Tagged TLBs in case that when switching

VMs the TLB will be flushed.


Memory Virtualization – in Practice In full virtualization, hypervisor traps every

action try to update page table. At once hypervisor traps the action, hypervisor can

take over.

In Xen paravirtualization, para-virtualized OS directly invoke hypercalls to ask hypervisor update the page table. Much faster.


Distributed Memory Virtualization – the Idea Pooling the virtualized memory

We can add nodes into our cloud to extend the memory capacity.

Breaking the bound of physical machines If an VM instance in a node need more memories, it

can get memories from other nodes.


Distributed Memory Virtualization – in Practice

Performance issue. Relatively very very high latency compare to local memories. Latency of Infiniband or 10G Ethernet : 1.07 ~ 2.6 µs. Latency of DDR3 SDRAM: 10.5 ns.

Page table for distributed environment adds even more overhead.

Therefore, mainstream hypervisors don’t support distributed memory virtualization, for now.


Summary

Some characteristics of cloud computing need virtualization to achieve.

Virtualization technology leads to better utilization and elastic deployment. It also leads to better business model.


Summary

Virtualization Approaches Full Virtualization : High compatibility, low

performance. Para-Virtualization : Need OS modified for VMM,

best performance. HAV : Need newer hardware, good compatibility,

good performance


Summary

Device Drivers needs virtualization as well. Rather than emulation a whole device, we can

implement a simple front-end in guest, and communicate with back-end device driver.

Memory Virtualization Performance critical. Lot’s new designs in CPU in order to optimization

memory related operations.


cloud operating system unit 09 cloud os core technology m. c. chiang department of computer science...

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