Transcript Study of Hurricane and Tornado Operating Systems

Study of Hurricane and Tornado
Operating Systems
By Shubhanan Bakre
Agenda
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A brief introduction
A brief idea about the underlying hardware
Architecture of Hurricane and Tornado
Scheduling
Processes in Hurricane and Tornado
Memory Management
File System Management
Input/Output Management
Introduction
• Hurricane and Tornado are microkernel based
operating systems.
• Hurricane is built for the Hector multiprocessor.
• Tornado is built for the NUMAchine
multiprocessor.
• Both these operating systems are built by the
Parallel Systems Group at the University of
Toronto.
The Hector Multiprocessor
The NUMAchine
• Consists of 64 processors
• Cache coherence hardware is present
• Processors are connected in a two level hierarchy
Architecture of Hurricane and
Tornado
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The operating system is divided into clusters.
A cluster is made up of three layers
A cluster can span more than one processors
All the operating system services are replicated to
each cluster
• It provides modularity to the operating system
• Clustering improves the scalability of the
operating system
Structure of A Cluster
Hierarchical Clustering
• Hurricane and Tornado use a single level of
clustering
• It provides the user with an integrated view of the
whole system
• Achieves tight coupling within the cluster
• Maintains loose coupling among the clusters
• It aims at achieving locality for data and code
• Improves concurrency
Hierarchical Clustering
• A cluster size of one mimics a distributed system
• A cluster size equal to the whole system size
behaves like a Shared Memory System
• Changing the cluster size affects system behavior
• Contention puts an upper bound on the size of a
cluster
• Need for consistency puts a lower bound on the
cluster size
Coupling Vs Cost
Scheduling
• Two level scheduling is used
• Within the cluster, the dispatcher is
responsible for scheduling
• The second level takes care of load
balancing
• It also decides the placement policy
• It takes decisions on migration and
replication
Processes
• Management of the shared memory.
• Use of locking mechanisms to provide
mutual exclusion.
• Processes can migrate to other clusters.
• Lock contention is reduced due to clustering
Processes
• Uses a hybrid lock which provides.
– Low latency where coarse grained lock is used.
– High concurrency where a fine grained lock is used.
• Uses deadlock avoidance strategy for handling
deadlocks.
• Inter-process communication takes place.
– Within the cluster using protected procedure calls.
– Between the clusters using message passing.
Processes: Protected Procedure
Calls (PPC)
• Aim of PPC is to
– Avoid accessing shared region.
– Avoid acquiring locks.
• Server acts as a passive object.
• The client moves from one address space to
another.
• A worker thread within the server takes care
of the client request.
Memory Management
• Supports traditional page based memory.
• Every process is provided a virtual address space
called Hurricane region.
• Takes care of the replication and page migration.
• Protocols used for cache coherence are
– Update protocol
– Validate Protocol
• Protocols used for replication are
– Degree of replication
– Replicate on write
Memory Management
• A Shared region is a shared data object
accessed by a task.
• Functions are provided to access these
shared region which include
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ReadAccess
ReadDone
WriteAccess
WriteDone
Coherence Protocols: Update
Protocol
• Consistency is maintained at WriteDone time
• Cache is invalidated for both ReadDone and
WriteDone
•This approach is simple but very inefficient.
Coherence Protocols: Validate
Protocol
• Consistency is maintained at the next “Access”.
• Checks whether the copy in cache is valid or not.
• Keeps a status vector for storing this information.
Replication Protocols
• Degree of Replication
– Checks whether the distance from the nearest
replica is within a threshold value
– If yes then replica is not created. Mapping is
done to that copy.
– If no then a new copy is created.
– Controls the degree of replication
Replication Protocols
• Replicate on Write
– Replicates data on write request.
– Can be efficient if the number of write requests
is greater than the number of read requests.
– Can turn out to be inefficient due to the number
of coherence operations required.
Hurricane File System
• Goals of the Hurricane File System (HFS)
– Flexibility – should support large number of
file structures and policies.
– Customizability – should allow the application
to specify the policy and the file structure to be
used.
– Efficiency – flexibility should be achieved at
little CPU and I/O overhead.
Hurricane File System
• Uses object oriented techniques.
• A Storage object forms the building block
of a file.
• Storage object is an encapsulated object
having member functions and data.
• The block storage object is the most
fundamental type of storage object.
• In that it stores the actual file data.
Hurricane File System
• Categories of Storage Objects
– Transitory Storage Objects
– Persistent Storage Objects
• Transitory Storage Objects are created at run time.
• Persistent Storage Objects once created remain
fixed and get stored to the disk.
• Persistent Storage Objects are stored in the same
way as file data.
Layers of the HFS
• Physical Server Layer
– It directs requests for file data to disk.
– It is responsible for policies related to disk
block placement, load balancing, locality
management and cylinder clustering
– All Physical Server Layer objects are persistent
– Example of Physical Server Layer Object
(PSO): read/write PSO
Layers of HFS
• Physical Server Layer Objects (PSO) are
further divided into
– Basic PSO classes
– Composite PSO classes
– Read/write PSO classes
Layers of the HFS
• Logical Server Layer
– Provides functionality which can be outside the
physical server layer and should not be in the
Application level library.
– All Logical Server Layer Objects (LSO) are persistent.
– Consists of various types of classes like Naming
classes, Access-specific classes, Locking classes and
Open authentication classes
– These objects can be used in hierarchical fashion.
Layers of HFS
Input/Output
• Alloc Stream Facility (ASF) provides the I/O
facility in Hurricane.
• It is designed in the application layer.
• Provides portability to the applications.
• Provides better interface to the programming
language.
• Improves performance by
– Reducing the amount of data copying.
– Reducing the number of system calls.
Alloc Stream Facility
• Consists of three layers
– The interface layer – implements the interface
modules.
– The backplane – contains all the code that is
common to rest of the two layers.
– The stream layer – interacts with the operating
system and manages buffering.
Conclusion
• Hierarchical clustering cannot be applied at
a finer level in Hurricane.
• Modularity in Tornado can be improved due
to object orientation.
• Due to different system architectures both
these systems are distinct.
Questions