TreadMarks: Distributed Shared Memory on Standard Workstations and Operating Systems Present By: Blair Fort Oct. 28, 2004

Overview Introduction and Motivation Implementation Experiments and Results Conclusions My two cents

Introduction Threadmarks is a Distributed Shared Memory system Unix workstations over an ATM or Ethernet network

Cluster Configuration

Distributed Shared Memory

Motivation No widely available DSM system Eliminate problems of other system  Bad portability  Bad performance  False sharing

Goals Ease of Use Portability Good Performance  Also show that it works for real programs

Overview Introduction and Motivation Implementation Experiments and Results Conclusions My two cents

Ease of Use Looks a lot like pthreads Implicit message passing Implicit process creation

Portability Only standard Unix System Calls  Message Passing  Memory Management

Performance False sharing Excessive message passing

Conventional DSM Implementation

Sequential vs Release Consistency Every Write is broadcasted More Message Passing Writes are broadcasted only synchronization points More Memory overhead

Read-Write False Sharing w(x) r(y) r(x) w(x)

Read-Write False Sharing w(x) r(y) r(x) synch

Write-Write False Sharing w(x) w(y) r(x) synch w(x)

Multiple-Writer False Sharing w(x) w(y) r(x) synch w(x)

Eager vs. Lazy RC Sends Messages at release of lock or at barriers Broadcasts Messages to all nodes Sends Messages when locks are acquired Message goes only to the required node

Eager vs. Lazy RC

Memory Consistency Done by creating diffs Eager RC creates diffs at barriers Lazy RC creates diffs at the first use of a page

Twin Creation

Diff Organization

Vector Timestamps w(x) rel acq w(y) rel p1 p2 p3 acq r(x) r(y)

Diff chain in Proc 4

Garbage Collection Used to merge all diffs – recover memory Occurs only at barriers All nodes that have a pages must have all diffs of that page.

Overview Introduction and Motivation Implementation Experiments and Results Conclusions My two cents

Testing Platform 8 DECstation-5000/240’s running Ultrix V4.3 Network:  ATM 100Mbps  Ethernet 10Mbps

Testing Programs Modified Water from Splash Jacobi TSP QuickSort ILINK

Unix Overhead

ThreadMarks Overhead

Network Comparison - Water

Lazy vs Eager RC

Message Rate

Data Rate

Diff Creation Rate

Overview Introduction and Motivation Implementation Experiments and Results Conclusions My two cents

Conclusions Automated Distributed Shared Memory system works for real programs! LRC improves performance over ERC for most cases

Overview Introduction and Motivation Implementation Experiments and Results Conclusions My two cents

My Thoughts Good design – promotes re-use Would like to see a comparison over hand- coding the message passing Why not a partial merging of diffs?

Comments/Questions