Dynamic Load Sharing and Balancing Sig Freund

Outline Introduction Distributed vs. Traditional scheduling Process Interaction models Distributed Systems Research Studies Guess about the Future? Questions

Introduction Load Sharing Load Balancing Static vs. Dynamic

Distributed vs. Traditional scheduling differences Communication overhead is non-negligible Effects of underlying hardware cannot be ignored Dynamic behavior of system must be addressed

Process Interaction models Precedence process model

Static Process Scheduling

Precedence Process Scheduling Extended List Scheduling Earliest Task First

Process Interaction models Communication process model

Process Interaction models Disjoint process model

Distributed System Difficulties Assumption of prior knowledge not realistic Use disjoint process model since we don’t know how they interact

Simple Heuristic Strategy Central Controller Process Maintain queue size of each processor Process arrive and depart asynchronously Assignment made to processor with shortest queue At completion, processor sends queue info

Process Migration Monitors processors assigned to processes Schedule is initiated by process departure instead of arrival Moves processes to achieve fairness Two common models ◦ Sender-initiated algorithm ◦ Receiver-initiated algorithm

Sender-initiated Algorithm Process wishing to off-load initiates Migrates process from heavily loaded processor to lightly loaded Requires three decisions ◦ Transfer policy ◦ Selection policy ◦ Location policy

Location Policy Random selection ◦ May cause chain effect of transfers Probe for candidate ◦ Probe limit ◦ Multicast

Receiver-initiated Algorithm Lightly loaded processor requests more work Same three decisions ◦ Transfer policy ◦ Location policy ◦ Selection policy Benefits ◦ More stable ◦ Perform better

Research Studies Dynamic load balancing in distributed computer systems with star topology[1995] Performance of dynamic load balancing algorithm on cluster of workstations and PCs[2002]

Sender-initiated Algorithm Compare load balancing policies for effective dynamic load balancing on the basis of decision strategy for job transfer and destination decision. ◦ FT ◦ RT ◦ ALBCI ◦ ALBCII [1995]

Sender-initiated Algorithm

Hybrid Load Balancing Algorithm Compare load balancing scheme for parallel depth first search on two systems. ◦ 6 Sun Workstations running Solaris ◦ 10 PC’s running Linux Round-robin work sharing Completely distributed system [2002]

Hybrid Load Balancing Algorithm

Current Challenges High reliance on central node High load systems require most communication resources Heterogeneous systems greatly complicate load balancing

Future System[2008] Board of Directors ◦ Small group of controlling nodes ◦ Number is dynamic ◦ Capable of splitting or combining ◦ Maintain shared historical data for better initial process assignment Worker nodes ◦ Specialized functions ◦ Reconfigurable (Time slice/Com polling)

References 1.Randy Chow and Theodore Johnson (1997),DISTRIBUTED OPERATING SYSTEMS AND ALGORITHMS 2. Xinda, M. I. (2002). PERFORMANCE OF LOAD BALANCING ALGORITHM ON CLUSTER OF WORKSTATIONA AND PCS. Algorithms and Architectures for Parallel Processing, Proceedings. Fifth International Conference on, (pp ). 3. Chong-Gun, L. K.-S. (1995). Dynamic load balancing in distributed computer systems with star topology. Distributed Computing Systems, 1995., Proceedings of the Fifth IEEE Computer Society Workshop on Future Trends of, (pp ). 4. Abraham Silberschatz, Peter Galvin, and Greg Gagne (2005) OPERATING SYSTEM CONCEPTS 5. Sig Freund (2008) FUTURE DISTRIBUTED OPERATING SYSTEM CONCEPT

Questions?