1. 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

2. 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

3. 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] [2] A system-level approach for memory robustness, ICMTD05 [3] Lifetime Reliability: Towards an architectural solution, IEEE Micro [4] 3

4. Hmm… My ATM Does Not Work4

5. 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

6. PCs/Laptops Not Far Behind
“Take-away something.” 6

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

8. 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

9. 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

10. 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