Current Work on MaCS

1
Current Work on MaCS

• S. Kannan, M. Kim, I. Lee,
• O. Sokolsky, and M. Viswanathan

2
Outlines

• Enhancing Monitoring Performance
• MaCS Applications
• Protocol monitoring
• Software usage monitoring

3
Overall Monitoring Structure

• Communication medium i,c
• Snapshot and buffer implementation s,p,w,r
• Evaluation of snapshot e2

• Overhead factors

4
Overhead Factors

• Instrumentation overhead
• p cost for a probe execution
• w cost for writing a snapshot into a buffer
• s size of a snapshot
• Communication overhead
• i cost for communication initialization
• c cost for 1 byte transfer
• Monitor overhead
• r cost for reading a snapshot from a buffer
• e2 cost for evaluating properties per a
  received snapshot

5
Enhancing Monitoring Performance

• Overhead due to monitoring
• Instrumentation overhead
• Communication overhead
• Monitor overhead
• Enhancing monitoring performance
• Reducing snapshot size
• Reducing snapshot extraction/exportation
  frequency
• Reducing evaluation cost

6
Reducing snapshot size

• A snapshot contains either
• variable id and corresponding value
• method id and beginning/ending flag
• Structure of a snapshot
• Compression of snapshots in the communication
  buffer
• decreases communication overhead but induces
  computation overhead

7
Reducing snapshot size (cont.)

• Reduce a frequency/size of time stamp
• Time stamp takes up-to 57 of snapshot size
• Reduce the frequency of time stamp attachment to
  the snapshot
• Sending time stamp w/ only relevant snapshots
• Periodic timing updates w/o time stamp attached
  to a snapshot
• Reduce the size of time stamp
• Smaller size representation (w/ assumption on the
  maximum interval between two consecutive
  snapshots)
• Coarse resolution

8
Reducing Frequency of Extraction

• Statically restrict scope in which variables and
  methods need to be monitored
• exgt monitoring a maximum balance in a bank
  account
• monobj double account.balance in
  account.deposit(double)
• class account
• double balance
• void deposit(double amount) balanceamount
• double withdrawal(double amount) balance -
  amount
• decrease instrumentation/communication/monitor
  overhead

9
Reducing Frequency of Exportation

• Export a snapshot only if the new value changes
  condition
• tradeoff between
• cost for detecting a change on a condition
• reduced communication/monitor overhead
• exgt
• condition c1 x lt 10
• property safe c1 c2 ...

10
Reducing the Evaluation Cost

• Observation
• Repeated patterns may be generated frequently by
  a target system in execution
• exgt int C.x is assigned with 1 frequently
• Evaluating properties can use a history table
  containing previous evaluation results as a cache
  for reducing evaluation cost
• analogy obtaining sin(x) by using a table
  containing pre-calculated values of sin(x)

11
MaCS Applications

• Artificial physics simulation
• Charon specification
• Protocol
• Software usage

12
Protocol

• Properties to check
• Correctness
• What a sender sends should be same to what a
  receiver receives
• Conformance to the specification
• Implementation should follow protocol handshake
  exactly
• Utilization
• Unnecessary handshake should not happen for
  performance
• Note. Bugs of Java Secure Socket Extension
  (JSSE) 1.0.1

Server
msg
sn
s1
Monitor
c1
cm
Client
msg
13
Software Usage Monitoring

• Software component usage is good information for
  several reasons
• Charging based on software usage
• Administration purpose
• Software optimization
• Current way of program auditing done by OS
• Based on only execution time and file accesses
  coarse and primitive
• Not adequate for knowing activity in detail
• ex. How many times and how long rendering is
  used in Adobe PhotoShop
• ex. How many times a patented encryption
  algorithm X is used among a set of encryption
  algorithms in Internet Explorer
• Finer level of auditing at run-time is desirable
• ex. Service fee at internet cafe