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EXTENSIBILITY, SAFETY AND
PERFORMANCE IN THE SPIN
OPERATING SYSTEM
Brian N. Bershad, Stefan Savage, Przemysław
Pardyak, Emin G¨un Sirer, Marc E. Fiuczynski,
David Becker, Craig Chambers, Susan Eggers
Presenter: Myeonwoo Lim
OUTLINE
1.
2.
3.
4.
5.
6.
Overview
Motivation
SPIN Architecture
Core Services
Performance
Conclusions
OVERVIEW

What is spin?

SPIN is a dynamically extensible operating system
that allows user applications to safely change the
operating system's interface and implementation.
Extensions are linked into the operating system
kernel at application runtime, enabling them to
access system services with low overhead.
OVERVIEW

Goals
SPIN combines research in systems, languages, and compilers to
achieve the three fundamental goals of modern operating systems.

Extensibility


Safety


Applications must be able to extend kernel functionality.
Access to system resources must be controlled at the same
granularity at which extensions are defined
Performance
Requires low-overhead in the extension mechanisms
 Application performance is the end goal

OVERVIEW

Approach for the goals

Co-location


Enforced modularity


Extensions are written in Modula-3, which enforces interface
boundaries between modules.
Logical protection domains


Extensions live in kernel space
Namespaces inside kernel, intra-domain communication
possible at cost of procedure call
Dynamic call binding

Extensions execute in response to system events.
MOTIVATION


SPIN is motivated by the need to support
applications that present demands poorly matched by
an operating system’s implementation or interface.
Related Work

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Hydra [Wulf et al ‘81]
Microkernels [Bershad et al ‘90]
Cross-Domain Communication [Hamilton & Kourgiouris]
“Little Languages” [Lee et al ‘94]
Code install in kernel at runtime [Heidemann & Popek
‘94]
Software fault isolation [Wahbe et al. 93]
Aegis[Engler et al. 95]
SPIN STRUCTURE

SPIN architecture provides a software
infrastructure for safely combining system and
application code.

Protection Model


Extension Model


supports efficient, fine-grained access control of resources
enables extensions to be defined at the granularity of a
procedure call
Relevant properties of Modula-3

Interfaces, type safety, automatic storage
management, objects, generic interfaces, threads, and
exceptions.
SPIN STRUCTURE
PROTECTION MODEL


Controls the set of operations that can be applied
to resources.
Capabilities: Unforgeable reference to a resource.
All kernel resources are referenced by capabilities
 Resources are protected to ensure that extension
reference the resources to which they have been
given access
 SPIN implements capabilities directly using
pointers
 A pointer can be passed from the kernel to userlevel applications as externalized references

SPIN STRUCTURE
PROTECTION MODEL

CONT’D.
Protection domains
Defines a set of names, or program symbols, which
can be referenced by code with access to the domain.
 A domain, named by a capability, is used to control
dynamic linking, and corresponds to one or safer
object files.
 Operations




Create: create a new domain
Resolve: dynamic linking
Combine: create a new aggregate domain
SPIN STRUCTURE
EXTENSION MODEL



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Provides a controlled communication facility between
extensions and the base system
Extensions in SPIN are defined in terms of events
and handlers
The primary right to handle an event is restricted to
the default implementation module for the event,
which is the module that statically exports the
procedure named by the event
Other modules may request that the dispatcher
install additional handlers or even remove the
primary handler
Dispatcher contacts primary implementation module.
If denied installation falls
If allowed, the implementation module can provide a
guard to be associated with the handler
CORE SERVICES
SPIN provides a set of core services that manage
memory and processor resources
 The core services provided by SPIN are

Extensible memory management
 Extensible thread management

CORE SERVICES
EXTENSIBLE MEMORY MANAGEMENT


A memory management system is responsible for
the allocation of virtual addresses, physical
addresses, and mapping between the two.
Components

Physical address service: controls use and allocation of
physical pages.

Virtual address service: allocates capabilities for virtual
addresses.

Translation service: expresses relationship between physical
and virtual addresses.
CORE SERVICES
EXTENSIBLE THREAD MANAGEMENT
Application can provide its own thread package
and scheduler that executes within the kernel.
 SPIN doesn’t define thread model, instead
defines structure upon which different threading
models can be implemented.
 SPIN use strands.
 Operations:

Block
 Unblock
 Checkpoint
 Resume

PERFORMANCE

Platform
SPIN runs on DEC Alpha platforms
 Measurements

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
DEC Alpha 133Mhz AXP 3000/400 works stations
Comparison system

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MEC OSF/1 V2.1 (monolithic operating system)
Mach 3.0
PERFORMANCE

Mirobenchmarks: Protected communication


SPIN performed better for both system calls and cross-address calls.
It’s in-kernel calls were significantly faster then either two of the
other methods
PERFORMANCE

Microbenchmarks: Thread Management

Thread performance in spin was better than that of
OSF/1 and Mach in the ping-pong and fork-join tests.
PERFORMANCE


Microbenchmarks: Virtual Memory
Reasons for outperform
SPIN uses kernel extensions to define application
specific system calls for virtual memory management.
 Virtual memory event is reflected to the application
through a fast in-kernel protected procedure call

PERFORMANCE

Networking: Network Latency and Bandwidth
SPIN shows better network latency and bandwidth
performance characteristics then OSF/1.
 The application code executes in the kernel, where it has
low-latency access to both the device and data.

PERFORMANCE

End to End Performance
SPIN utilizes half of the hardware as compared to OSF/1 for
the same client load.
 SPIN tries to avoid double buffering between OS and
application.

CONCLUSIONS
SPIN achieves performance in an extensible
system without sacrificing safety.
 SPIN provides a set of efficient mechanisms to
extend services along with basic set of core
services.
 Programming languages with the appropriate
feature support can be used to construct future
operating systems

QUESTIONS?