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Extensibility, Safety and
Performance in the SPIN
Operating System
Dave Camarillo
What is SPIN?
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SPIN is an experimental operating
system that uses a non-traditional
structure to provide extensibility, safety
and performance.
SPIN allows for modules to interact
with the OS so as to gain performance
benefits of specialization and retain the
generalization of a generic OS.
Why was SPIN Created?
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Most OS’s can run many applications
with acceptable performance.
Other OS’s can run a few applications
with excellent performance.
It’s difficult or impossible to find OS’s
that can do both (but it would be nice).
Why was SPIN Created? (cont.)
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An attempt to make a general purpose
OS that can run all applications well.
Provide a OS that is extensible so new
functionality can be added with the
best performance characteristics.
Language for Security
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SPIN uses language functionality to for
security.
Relies on Modula-3’s interfaces, type safety
and automatic storage management.
All code is implemented within modules,
which are type checked at compile time and
can only be manipulated thru safe interfaces
that are published.
Protection Domains
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A protection domain consists of a set of
names and/or symbols that can be
referenced by code with access to that
domain.
Only Modula-3 signed modules are given
un-checked access to a protection domain.
Modules that are not signed are checked by
assertion (more time consuming, but
ensuring safety).
Module/Domain Exporting
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Module creates an explicit domain.
Modules uses the in-kernel name
server to advertise it’s availability.
Modules can register an authorization
method, allowing a module to restrict
access to it’s functionality.
The Extension Model
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Event listeners can be registered by
modules with the event dispatcher.
When an event occurs, the dispatcher
will call the registered procedure in the
module to handle the event.
Extensions
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Processes install additional extensions into
the kernels address space to avoid the
future need to make extra kernel calls.
Kernel verifies the Modula-3 signatures of
the extensions.
Process
Kernel
Std Ker
Modules
Process
Process
User
Mod 1
User
Mod 2
Hardware
User
Mod 3
Standard Extensions in SPIN
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Memory Management
Thread Management
Memory Management
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Three Components: physical storage,
naming, translation
Physical Address Service controls the use
and allocation of physical pages.
Virtual Address Service creates virtual
addresses indicating their address space,
length and identifier.
Translation Service expresses virtual to real
address mappings, utilizing the MMU
Thread Management
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SPIN doesn’t define thread model,
instead defines structure upon which
different threading models can be
implemented.
SPIN provides Strands
They’ve used OSF/1 kernel threads,
C-Threads and Modula-3 threads in
SPIN.
SPIN Performance
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System Size
Micro benchmarks
Networking
End-to-end performance
Performance: Micro
Benchmarks, Communication
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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: Micro
Benchmarks, Threads
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Thread performance in SPIN was
better then that of OSF/1 and Mach in
the ping-pong and fork-join tests.
Performance: Micro
Benchmarks, Virtual Memory
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SPIN uses kernel extensions to define
application-specific system calls for
VM management.
The multiple application-kernel
interactions are reflected to the
application by fast in-kernel modules,
avoiding the need to use traps or
messages.
Performance, Networking,
Latency & Bandwidth
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SPIN shows better network latency
and bandwidth performance
characteristics then OSF/1.
Largely due to processing of network
traffic within kernel as opposed to in
application.
Performance, End to End
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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
The use of co-location, loadable
modules, protection domains and
dynamic call binding can allow an OS
to be minimal, flexible, extensible and
efficient.