Scott Mahlke University of Michigan Top 5 Reasons Reliability is the Biggest Fallacy in Computer Architecture Research Scott Mahlke University of Michigan Thanks to Jason Blome, Shuguang Feng, and Shantanu Gupta for putting their research on reliable systems on hold to help with this presentation. 1

Still a need for high reliability designs for mission critical systems Disclaimer Still a need for high reliability designs for mission critical systems Space shuttle, airplanes, etc. Cost is not an issue – use high degrees of redundancy Legacy code was not developed to give tools deep knowledge about the computation being performed. E.g., source code does not express high-level properties and assumptions The question is how to go from parallel algorithms to parallel machine code I would like to convince you reliability is a fallacy for mainstream computer systems used in consumer/business electronics* *The speaker may not agree with this position 2

Reason 1: It’s the Software, Stupid! Reliability of softwares that have a large consumer base (like Windows) has not shown improvement. The failures per billion hours of operation in Windows are an order of magnitude higher than corresponding value for hardware components. In the data shown here, the software errors are mostly of transient nature, while the hardware errors are permanent. “Mature OS can have an MTTF measured in months, while newer OS may crash every few days.” – Peter Chen: Reliability Hierarchies, 1999 HOT OS. Sources: [1] www.nstl.com [2] A system-level approach for memory robustness, ICMTD05 [3] Lifetime Reliability: Towards an architectural solution, IEEE Micro 2005 [4] www.calce.umd.edu 3

Hmm… My ATM Does Not Work 4

Reason 2: Disposable Electronics “The average working life of a mobile phone is 7 years, but the average consumer changes their mobile every 11 months. 5

PCs/Laptops Not Far Behind “Take-away something.” http:/ieeexplore.ieee.org/iel5/9100/28876/01299720.pdf 6

Reason 3: A Transient Fault is About As Likely As … 7

Reason 4: Does Anyone Care? Which is flawed? Can a human identify errors in video, images, or sound? Glitches are accepted by the consumer (dropped cell calls) Natural redundancy and resiliency in software 100% reliable operation of hardware is not important or worth extra cost in many situations 8

Reason 5: This Problem is Better Solved Closer to the Circuit Level Intra-die variations in ILD thickness Electromigration in copper Error_L Error comparator RAZOR FF clk_del Main Flip-Flop clk Shadow Latch Q1 D1 1 Lower overhead Many designs benefit In-situ solutions naturally handle variation 9

Some Hope? What if we assume reliability is a looming problem. Then we need solutions that are: Low overhead, high rate of return solutions Joint circuit/architectural techniques Domain specific solutions – know thy customer Reliability features provide other benefits Its not just a tax The bottom line 10