Computer Science 313 – Advanced Programming Topics

Tom Cargill The first 90% of the code accounts for the first 90% of the development time. The remaining 10% of the code accounts for the other 90% of the development time.

Let’s Get Coding  Who will write next lab in assembly?  Can only use assembly code for entire lab pushl %ebp movl %esp, %ebp subl $24, %esp movl 8(%ebp), %eax movl %eax, -4(%ebp) cmpl $0, -4(%ebp)

Let’s Get Coding  Who will write next lab in assembly?  Can only use assembly code for entire lab  During the first pass, apply standard optimizations pushl %ebp movl %esp, %ebp subl $24, %esp movl 8(%ebp), %eax movl %eax, -4(%ebp) cmpl $0, -4(%ebp)

Let’s Get Coding  Who will write next lab in assembly?  Can only use assembly code for entire lab  During the first pass, apply standard optimizations  Every method should be tuned to maximize branches pushl %ebp movl %esp, %ebp subl $24, %esp movl 8(%ebp), %eax movl %eax, -4(%ebp) cmpl $0, -4(%ebp)

Let’s Get Coding  Who will write next lab in assembly?  Can only use assembly code for entire lab  During the first pass, apply standard optimizations  Every method should be tuned to maximize branches  Necessary to achieve top performance pushl %ebp movl %esp, %ebp subl $24, %esp movl 8(%ebp), %eax movl %eax, -4(%ebp) cmpl $0, -4(%ebp)

Promise of Perfect Debugging  Programs just λ-calculus equations  Use Java, but instead prove program correct  Translate program into λ-calculus  Specify theorem & prove program correctness

Fewest Lectures Ever

Why Isn’t This Done?  Almost never use these techniques  Low-level device drivers use some C (or similar)  Rare for partial proof of correctness to be used  Simple result from easy cost-benefit analysis  Techniques requires massive amounts of time  Time is money; these are very, very expensive  The provided benefits just not worth it

What’s The Secret? How do I know when to optimize? I need to know. Please, please, please?

Problem is Universal  Frequent need to make optimal decision  Using reagents during chemical synthesis  Take power plant offline & perform maintenance  Fastest torrent from which to download  Cannot optimize everything  Instead we only focus efforts where it matters

Problem is Universal  Frequent need to make optimal decision  Using reagents during chemical synthesis  Take power plant offline & perform maintenance  Fastest torrent from which to download  Cannot optimize everything  Instead we only focus efforts where it matters But how can I know what is important?

Are Graphics Important?  Rewrite Swing to improve its performance?

Are Graphics Important?  Rewrite Swing to improve its performance? Hells, yes. We need 60 fps for new games.

Are Graphics Important?  Rewrite Swing to improve its performance? Hells, yes. We need 60 fps for new games. %#$ no. What does it do for search speed?

Critical Paths  All that is important is code along critical path  Determines time needed and not just the fluff  Graphics are not critical for Google  Major graphics improvements are nice…  …but have zero affect on search times  Bungie’s critical path is graphics package  Games performance limited by graphic times  Would hate GPU for search – slows them down

Guess the Critical Path $ java -Xprof edu.canisius.ann.Network Flat profile of 16.4 secs (956 total ticks): main Compiled + native Method 35.6% Neuron.getWeightedError 21.1% Neuron.updateWeights 13.0% Network.trainNetwork 9.5% java.lang.StrictMath.exp 9.5% Neuron.compute 4.5% Network.setNetworkInput 3.6% Network.runOneInput 2.0% java.util.ArrayList. 0.8% Network.main 99.6% Total compiled

Still a Cost-Benefit Trade Great. More useless geekery. When will it make a difference? When is it worth my time?

Amdahl’s Law  Determines how much faster program can go  Use this to answer question that matters  Speedup calculated by this equation  Speedup of 2 means program twice as fast  Need 1 / 10 the time, 10 is speedup factor of approach  When speedup is 1, time taken unchanged  Speedup of ½ == twice as long as past approach

Amdahl’s Law  Determines how much faster program can go  Use this to answer question that matters  Speedup calculated by this equation  Speedup of 2 means program twice as fast  Need 1 / 10 the time, 10 is speedup factor of approach  When speedup is 1, time taken unchanged  Speedup of ½ == twice as long as past approach (But usually say slowdown factor of 2)

Amdahl’s Law  Determines how much faster program can go  Use this to answer question that matters  Speedup calculated by this equation  Speedup of 2 means program twice as fast  Need 1 / 10 the time, 10 is speedup factor of approach  When speedup is 1, time taken unchanged  Speedup of ½ == twice as long as past approach (But usually say slowdown factor of 2) (Or hide report that shows this sucks)

Amdahl’s Law Equation  %changed of time in methods to be optimized  Expressed as decimal between  All other time from run is %unchanged  Another decimal from 0 – 1 you FAIL  If %changed + %unchanged ≠ 1, you FAIL

Applying Amdahl’s Law  Made getWeightedError twice as fast  Speedup changed = 2, since now twice as fast  Took 16.4 seconds before, what will it take now?  Get execution times using java –Xprof 35.6% Neuron.getWeightedError %changed = %unchanged = = 0.644

Amdahl’s Law Speedup = 1.21

Applying Amdahl’s Law  Move Neuron.compute off critical path?  Removes it from program execution time  Speedup changed = ∞  Get execution times from java –Xprof 9.5% Neuron.compute %changed = %unchanged = = 0.905

Amdahl’s Law Speedup = 1.10

What Amdahl’s Law Means

For Next Class  Lab #2 on web/Angel in 1 hour  I will be in lab from – feel free to stop by  Read pages 37 – 55 in book  Get back into code & design patterns  How could we handle 1-to-many communication?  Why not have cycles in UML class diagram?  What is secret to Lindsay Lohan's success?