Power Efficient Comparators for Long Arguments in Superscalar Processors
description
Transcript of Power Efficient Comparators for Long Arguments in Superscalar Processors
![Page 1: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/1.jpg)
ISLPED 2003
Power Efficient Comparators for Long Arguments in Superscalar Processors
*supported in part by DARPA through the PAC-C program and NSF
Dmitry Ponomarev, Gurhan Kucuk, Oguz Ergin, Kanad Ghose Department of Computer Science
State University of New YorkBinghamton, NY 13902-6000
http://www.cs.binghamton.edu/~lowpower
International Symposium on Low Power Electronics and Design (ISLPED’03), August 27th 2003
![Page 2: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/2.jpg)
ISLPED 2003
Outline
Motivations8-bit comparator designs
Traditional ComparatorDissipate on Match Comparator (ICCD’02)
32-bit Comparator DesignsResults : Application to the Load-Store QueueConclusions
![Page 3: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/3.jpg)
ISLPED 2003
Motivation
Equality comparators are very pervasive in today’s superscalar datapaths.
Wake-up logic of the Issue QueuesDependency checking logicLoad-Store queuesTranslation Lookaside Buffers (TLB)CachesBranch Target Buffers (BTB)
![Page 4: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/4.jpg)
ISLPED 2003
Motivation (continued)
Traditional comparators dissipate energy on mismatches in any bit position of the arguments In many cases, mismatches are much more frequent than matches
Issue queue : Only 3% of all comparisons result in a match (Ergin et.al. , ICCD’02)
For energy efficiency, dissipate-on-match designs can be considered
![Page 5: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/5.jpg)
ISLPED 2003
Traditional 8-bit Pull-Down Comparator
precharge
Evaluation
![Page 6: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/6.jpg)
ISLPED 2003
Dissipate-on-Match Comparator (DMC, ICCD’02)
Propagation Precharge
Discharge
Evaluation
![Page 7: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/7.jpg)
ISLPED 2003
Use of the Long Comparators
Load-Store queues – to allow loads to bypass earlier storesTLBs – for associative lookupCaches – for associative lookupBTBs – for associative lookup
![Page 8: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/8.jpg)
ISLPED 2003
Traditional 8-bit Pull-Down Comparator
![Page 9: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/9.jpg)
ISLPED 2003
Dissipate-on-Match Comparator (DMC)
![Page 10: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/10.jpg)
ISLPED 2003
Comparison of larger operands : Some Alternatives
~270 ps ~270 ps
~270 ps >400 ps
>400 ps
![Page 11: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/11.jpg)
ISLPED 2003
Choosing the Right Alternative
Need to consider impact on :DelayEnergy
Have to look at distributions of bit values that are comparedMore than one alternative may be acceptable
![Page 12: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/12.jpg)
ISLPED 2003
Experimental Setup (AccuPower, DATE’02)
CompiledSPEC
benchmarksDatapath
specs
Performance stats
VLSI layoutdata
SPICEdeck
SPICE
MicroarchitecturalSimulator
Energy/PowerEstimator
Power/energystats
SPICE measures ofEnergy per transition
Transition counts,Context information
![Page 13: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/13.jpg)
ISLPED 2003
0.4%
32.5%
22.4%23.7% 21.0%
8.2%
60.5%
8.7%14.0%
8.6%
68.1%
2.8%1.9%4.7%
22.6%
70.1%
4.1%1.7%0.7%
23.5%
0%
10%
20%
30%
40%
50%
60%
70%
80%
0 1 2 3 4
Number of matching bit pairs in each of the 4 8-bit groups
group of bits 0-7
group of bits 8-15
group of bits 16-23
group of bits 24-31
Matching Statistics of 32-bit Addresses in the LSQ
![Page 14: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/14.jpg)
ISLPED 2003
Dissipate-on-Match Comparator (DMC)
![Page 15: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/15.jpg)
ISLPED 2003
Matching Statistics of 32-bit Addresses in the LSQ
0.4%
32.5%
22.4%23.7% 21.0%
8.2%
60.5%
8.7%14.0%
8.6%
68.1%
2.8%1.9%4.7%
22.6%
70.1%
4.1%1.7%0.7%
23.5%
0%
10%
20%
30%
40%
50%
60%
70%
80%
0 1 2 3 4
Number of matching bit pairs in each of the 4 8-bit groups
group of bits 0-7
group of bits 8-15
group of bits 16-23
group of bits 24-31
![Page 16: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/16.jpg)
ISLPED 2003
Energy savings in comparison of longer operands
19% Energy Increase 19% Energy Savings
![Page 17: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/17.jpg)
ISLPED 2003
Main Results
We discussed some energy-efficient 32-bit wide comparator designs
19% comparator-related energy reduction in LSQ is achieved by using a hybrid design (3 TRADs + 1 DMC) compared to the use of 4 TRAD comparators
Results can be extended to TLBs and BTBs
![Page 18: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/18.jpg)
ISLPED 2003
THANK YOU !
*supported in part by DARPA through the PAC-C program and NSF
LOW POWER RESEARCH GROUP Department of Computer Science
State University of New YorkBinghamton, NY 13902-6000
http://www.cs.binghamton.edu/~lowpower
International Symposium on Low Power Electronics and Design (ISLPED’03), August 27th 2003
![Page 19: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/19.jpg)
ISLPED 2003
Timing Diagrams
![Page 20: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/20.jpg)
ISLPED 2003
32-bit Matching Statistics: LSQ
0%
10%
20%
30%
40%
50%
60%
70%
80%
0 1 2 3 4 5 6 7 8
group of least significant 8 bits
group of bits 8-15
group of bits 16-23
group of most significant 8 bits
![Page 21: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/21.jpg)
ISLPED 2003
Traditional 8-bit Pull-Down Comparator
![Page 22: Power Efficient Comparators for Long Arguments in Superscalar Processors](https://reader034.fdocuments.us/reader034/viewer/2022050821/5681675c550346895ddc27ed/html5/thumbnails/22.jpg)
ISLPED 2003
Pass Logic, Single-Stage Comparator (PLSSC)