Presentation on theme: "Why everything I learned at Leeds in 1972 is no longer true! Andrew Herbert 30 th March 2007."— Presentation transcript:
Why everything I learned at Leeds in 1972 is no longer true! Andrew Herbert 30 th March 2007
Personal Computing at Leeds (late 1960s)
Rethinking software In the 1970s, computer software was designed in large part to overcome hardware limitations In the 21st century, many of these limitations no longer apply. We have an abundance of computing resources This is changing how we think about software
Caution Much of what I will say relates primarily to personal computing There are many computer applications that are still held back by hardware Large server systems such as Google or Hotmail High Performance Computing applications for science, such as genomics, computational physics and chemistry
Moore Law (1967) Not really a law, but an observation, intended to hold for...the next few years… (N t /A) t1 = (N t /A) t0 * 1.58 t 1 -t 0 (t in years) N t : number of transistors; A: area Moores observation has held for 35 years and has sustained the personal computer industry NB Moores Law is about transistor count, not speed…
Implications for Processors More complex designs: rich instruction sets, pipelining, out of order execution, speculative execution, caching More than one processor on a chip (homogeneous multi-processor) More than one processor on a chip, with specialized functions, Graphics performance is improving much faster than CPU performance
… we see a very significant shift in what architectures will look like in the future... fundamentally the way we've begun to look at doing that is to move from instruction level concurrency to … multiple cores per die. But we're going to continue to go beyond there. And that just won't be in our server lines in the future; this will permeate every architecture that we build. All will have massively multicore implementations. Intel Developer Forum, Spring 2004 Pat Gelsinger Chief Technology Officer, Senior Vice President Intel Corporation February, 19, ,000 1, Power Density (W/cm 2 ) Pentium ® processors Hot Plate Nuclear Reactor Rocket Nozzle Suns Surface Intel Developer Forum, Spring Pat Gelsinger CPU Clock Speed DRAM Access Speed Today's Architecture: Memory access speed not keeping up with CPU clock speeds Modern Microprocessors - Jason Patterson (MHz) Speed (MHz) 10,0001, CPU Clock Speed DRAM Access Speed Todays Architecture: Heat becoming an unmanageable problem! Intel Cancels Top-Speed Pentium 4 Chip Thu Oct 14, 6:50 PM ET Technology - Reuters By Daniel Sorid Intel …canceled plans to introduce its highest-speed desktop computer chip, ending for now a 25-year run that has seen the speeds of Intel's microprocessors increase by more than 750 times. Memory Wall ~90 cycles of the CPU clock to access main memory! The Intel perspective…
Obsolete software idea 1: Single-threaded programs With uniprocessors, there is no compelling reason to try to use parallelism and write concurrent programs Your program will probably run slower due to thread creation, destruction, and switching Your program is harder to debug (Heisenbugs) Now we dont have a choice! Attempts to tease the parallelism out of a sequential program automatically havent worked out very well We need better education, better languages, and better tools, since building concurrent programs is hard Data driven computation - e.g. Map-Reduce
Obsolete software idea 2: Low-level programming languages Errors in handling array and heap storage are one of the leading causes of system unreliability in C and C++ Switching to languages like Java and C#, which provide automatic storage management, makes many types of errors impossible Until recently, programmers argued that these languages were too expensive in space and time Today, neither is an issue High level languages also allow programs that are easier to understand (and maintain) This is a high cost to the industry, since software evolves Functional programming finally comes of age?
Moores Law for Primary Memory Capacity improvement: 1,000,000 X since 1970 Bandwidth improvement: 100 X Latency reduction: only X Dealing with latency is the largest problem for a computer system designer
Obsolete software idea 3: Dynamic Paging / Backing Store Originally used to compensate for expensive, small main store Later extended to increase address space and to add protection Today, slows systems down, because of disk and providing enough real memory is inexpensive Yet all major operating systems use it Although you can turn off paging in Windows Increasing use of modern programming languages is also reducing the need for paging But virtualization for controlled resource sharing and resource separation is very important!
Software Complexity Complexity of developing, testing and supporting large scale software systems continues to escalate Source: Capers Jones, Estimating Software Costs, pg. 140 Capers Jones, Patterns of Software Systems Failure & Success 100%90%80%70%60%50%40%30%20%10%0% M10M Todays Software Development Process (Large Projects): Only 13% of projects are on time! Lines of Code % of Projects Early On-time Delayed Canceled100%90%80%70%60%50%40%30%20%10%0% M Todays Software Development Process (Medium/Large Projects): Only 18% of time spent on coding, 35% debugging! Lines of Code Documentation Support and Management Coding Finding & Removing Defects % of Effort by Task
Obsolete software idea 4: Verifying software quality by testing Testing is needed, but has limits: Hard to find certain types of problems (e.g. concurrency) Huge number of configurations is daunting Need more use of formal methods Mathematical model of system: specification Automated verification of software implementation Used to be impractical due to state space size explosion and CPU speeds Now routinely used in hardware design, where the cost of a bug is much larger Increasingly used in Microsoft development
Source: Sharad Malik (Princeton) – CAV invited talk Capacity Growth in Proof Engines for Propositional Logic
Source: Sharad Malik (Princeton) – CAV invited talk Capacity Growth in Proof Engines for Propositional Logic
Storage 30GB Personal file systems TerraServer - 5TB SkyServer – 40TB
Obsolete software idea 5: Hierarchical file systems Originally introduced to improve access efficiency and to give users a familiar metaphor (the office file cabinet with folders) Today, it has serious problems A clean install of Windows and Office has 45,000+ files The structure chosen by a person today will not be appropriate in six months Need a new way to organize things so we dont drown in information when we have a personal terabyte
New Ways of Organizing Files Full text indexing Microsoft Vista desktop search Extend to audio and handwriting Object recognition for image and video search Huge opportunities for personalization and exploiting context Timelines, work flow discovery and IM buddies Location awareness Network location, GPS etc
Example – Visual Summary Thumbnail Viewer - Win XP Tapestry Viewer Images in a folder
The Perfect Tapestry or Photo Collage System Input Images - Compose new image (Graphics) - Semantic inference Background Object People Object Recognition and Detection Flowers Rest
The MSR Cambridge Digital Tapestry [Rother, Kumar, Kolmogorov, Blake; CVPR 05] Objective: Choose informative, representative parts from many images and place them realistically Objective: Remove any visual seams Contributions: Novel problem formulation Extension of optimisation technique Novel membrane blending based on [Perez, Gangnet, Blake Siggraph 03] Block Tapestry Digital Tapestry Input Images
Obsolete idea 6: Computer monitors (screens) on desks What happens when display real-estate is free? What happens when dynamic displays are as ubiquitous as conventional signage, or whiteboards? What happens when displays can be as large as your wall? What happens when displays are as thin as your wallpaper? What happens if your cell phone has an A3 display, yet retains portability? What happens when all of this is factored in to other trends (wireless, speed, cost, …)?
New models of interaction Combine new display formats with machine perception Handwriting, gesture – Tablet PC Speech Touch Scanning / Recognition Physical objects The future is interactive surfaces
Obsolete idea 7: Standalone computers Electronics and photonics provide ever more bandwidth 1.36Tb/s femto second networks running now in the laboratory Wireless networking becoming ubiquitous Increasing bandwidth, decreasing power consumption, better spectrum optimization Everything is interconnected And therefore more complex… The computer is no larger the system boundary Tension between server versus client oriented computing models: rich vs. thin client, services vs. products vs. free (with adverts), centralized vs. peer to peer sharing and collaboration NB Latency
Obsolete idea 8: Artificial Intelligence Real world is too complex to model using formal data structures Statistical models for computing with hypotheses turn out to be very robust and applicable to a wide range of problems Machine Learning Train an algorithm with labelled data Classify new data using trained algorithm Bayesian and Markov models dominate Contrast with rule-based AI Machine perception, but not understanding Increasingly practical due to both Moores law and better algorithms
Machine Translation Microsoft data-driven machine translation system Hybrid system uses symbolic and statistical techniques Learns translation correspondences automatically from over a million bilingual sentence pairs Builds on same technology used in grammar checkers & other Microsoft products
Translating Knowledge Bases Automatically translate Microsoft on-line Knowledge Base into multiple languages Previously English-only Only a small set of crucial articles (about 5% of total) had been translated Size (140,000 documents, 80 million words) made human translation economically infeasible Spanish online today, French and German coming… SP KB (5 mos) US KB (5 mos) % of customers who are satisfied with KB 79%73% % of customers who could solve their issues using KB 55%57%
What Might Stop Moores Law? Physical limits Atoms are too large, and light is too slow Today, the problem isnt making the transistors faster, its the time for signals to propagate on the wires (latency again) Power. Lots of transistors => lots of power. Cooling is hard Design complexity Designing a billion-transistor chip takes a large team, even with good design tools The junk DNA problem Economics Factories are very expensive Latency: See D. Patterson, Latency Lags Bandwidth, CACM, October 2004
Conclusions Hardware has evolved rapidly We havent exploited it as well as we should May be some of the stuff I learned at Leeds was useful after all!