Evaluations

Yang YU (yyu@cs.ucsd.edu)
Thu, 04 May 2000 08:16:52 -0700

Distributed V Kernel:
Distributed V kernel is pure message oriented. It is used for
communication and data sharing in a local network where
all the workstations are diskless.
There are many advantages of diskless workstations such as lower
hardware cost and simpler maintainance,consistency.
but many people may think that the cost of network file access is huge.
However, The paper shows that
1. Diskless workstations can access remote files with minal
peformance penalty.
2. V message facility can be used to access remote files at a cost
almost the same as that of a specialiezed file access protocol

The primitives used use V kernel:
send, receive, reply, setpid, getpid
receive withSegment, reply withsegment, moveto, movefrom.
Messges are fixed length. While dat transfer operation is for larger
data transfer.
ReplyWithSegment and ReceiveWithSegment are used for minimize the
overhead of file transfer.

Features of implementation:
1. remote opertions are implemented at the kernel level
2. Interkenel packets use raw Ethernet datalink level, thus lowering
the overhead
3. reply-response nature of a reply acts as the acknowledgement
4. Single ack for a serie of data transfers
5. Process is named globally, a pid consists of machine id and local
process id.

The paper does a lot of analysis on the comparsion between network
file access and local file access,
remote kernel operation and local kernel operation, and concludes that
1. The network penalty is low.
2. There is a lower bound for any network access method, and
Distributed V is performance is near the bound.

Sprite:

Sprite is a distributed operating system that provides a single
system image to a cluster of workstations. It provides very
high file system performance through client and server caching. It has
process migration to take advantage of idle
machines.
It notices the trends in Computer Tech at that time(proved to be
true):
network , larger memory, and mulitprocessors.
These trends drive them to design the Sprite.
The interface of Sprite is almost the same as BSD UNIX, except:
transparent network file access, sharing writable memory between
processes on the same workstation, and process migrating to take
advantage of idle machines.
However, the kernel has been changed in Sprite a lot, including :
RPC allowing kernel on one workstation to invoke a process on
another.
Use prefix table to maitain name space
Caching file data on both server and client machines.
Use ordianary file are used by virtual memory to back storage.

--
Yang Yu
Department of Computer Science and Engineering
University of California, San Diego