1. Parallel ClockDesigner
Andrew Menard
Final Project
Spring 2002

2. The Problem
Distribute a clock signal from one source to a large number of latches using a tree.
Delay must be the same on every path through the tree.
Each branch must satisfy minimum and maximum size constraints.
Need to minimize resources used.

3. Initial algorithm
Add latches to a net until it violates a constraint, then create another net.
This results in a solution which is legal but suboptimal.
This legal solution can be handed to a refinement optimizer which will improve it.

4. Serial refinement optimizer
For each pair of nets, check whether there is any combination of latches that can be swapped between them that will make the larger one smaller
Repeat several times over the set of nets, so that any pair of nets is refined several times.

5. Parallel Refine Optimizer
Mother process spawns one child process per processor.
Mother process sends out a net and a list of adjacent nets to each thread, repeats.
Child process spins waiting for data, optimizes that net with list of adjacent nets, then waits again.

6. Complications
Child processes have to lock nets they are working on; a significant time sink.
Different pairs of nets can take wildly different amounts of time; some serialization at the end of each job.
Starting threads is expensive.

7. Results 20% Speedup in 4-processor version over serial version
Negligible change in memory
Scheduler matters a lot