1. ISCA 2005 Panel
Guri Sohi

2. Reliable software for unreliable hardware
2015 Code
Reliable software for unreliable hardware
Lots of redundant computation
“Probabilistic” vs. deterministic applications
Dependences and “incorrect computation” may or may not impact outcome
Heavy use of object-oriented programming style
Well-behaved and isolatable blocks of code

3. Parallelism Opportunities (4-5X each)
Extra functionality in applications
e.g., for reliability
Newer applications/algorithm/computation styles
e.g., “possibly incorrect” computation on multimedia data
New models for parallelization of traditional (sequential) code
Remember programming style

4. Models for Sequential Parallelization
Control-driven speculative parallelization
A.k.a multiscalar, transactions, etc.
Data-driven speculative parallelization
E.g., program demultiplexing

5. Program Demultiplexing
PD Runtime
M91()
M42()
M41()
Sequential Program
Out-of-order execution of program functions/methods
FU = processor
Instruction = Function

6. Program Demultiplexing
Sequential
Execution
Demultiplexed
Execution
Trig. Handler
On Trigger - Execute
M5()
On Call
- Use
M5()
Triggers
- Usually fires after data deps for M are satisfied
Need hardware to check this
Case Study
Small and specialized methods
Identifiable triggers

7. Program DemultiplexingY X
/ (20% overheads)
Time
1.2 Y X
15%
29%
15%
32%
33%
30%
25%
60%
10%
25% 5%
% of dyn. instructions contributed

8. Parallelism for 2015 Processors
We will have more opportunities for
innovation that we have ever had
before