Douglas Lacy & Daniel LeCheminant CS 252 December 10, 2003 AVID: Breaking Processors for Increased Performance & Reduced Power Consumption Douglas Lacy & Daniel LeCheminant CS 252 December 10, 2003

Background Todd Austin’s DIVA paper DIVA dynamically verifies all instructions, guarding against transient and permanent faults Austin speculated that DIVA could allow throttling of processor clock speed AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Background / Motivation DIVA: maintains correctness even with malfunctioning hardware Is there a way to “break” the core processor in such a way as to optimize it? Remove rarely-used components? Reduce tolerance in clock cycle, voltage, etc? May be possible to dynamically alter processor to be only as correct as necessary AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Motivation Some components of processors exist to ensure correctness in rarer cases May waste resources and cycles to check these cases With DIVA, we can ignore them, mostly “Rare” is variable Could be lazy with some computations, need to be more strict with others Which are possible is dependent on program AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Motivation cc1 anagram compress % Loads 23% 24% 21% % Stores 14% 10% 37% 33% 36% AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Motivation Specifically, what can we remove/throttle? Memory disambiguation Branch prediction Branch checking Exceptions Long-latency operations (multiply & divide) Rare instructions? Prefetching AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Proposal: AVID AVID: Architecture that Varies, Input Dependent Use a DIVA unit to provide verification, and also feedback to the core processor Can dynamically throttle operations from most time/power-consuming and correct to least consuming and sometimes incorrect Won’t require much more hardware than standard DIVA AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

AVID! AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

More AVID Branch predictors Multiply/Divide Loads Static, bimodal, 2-level, hybrid Multiply/Divide Truncate inputs, run for fewer cycles Loads Allow them to proceed past unresolved stores Clock cycle throttling Start fast, reduce speed if errors crop up AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Methodology Simulate in SimpleScalar Base architecture: Standard DIVA Modify simple scalar to include a core & DIVA unit Modify base architecture into AVID DIVA catches all errors so processor is still functional & reliable AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Comparison Run benchmarks on both architectures & compare performance (SPEC or similar) CPI: Read from simulator output Exec. Time: Total cycles * cycle time Power Consumption Total cycles * constant + branch predictions * constant for type of pred. Amount of hardware AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Results: CPI in Best Case cc1 anagram compress Base 1.0890 0.4985 0.5833 No Load Stalls 1.0879 0.4982 0.5815 Reduced Multiply 0.4984 SimpleScalar run with relaxed constraints without producing errors AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Results: Power Consumption prog Base Bimodal 2-Level Dynamic AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Conclusions No long benchmarks successfully run Preliminary results promising in some areas, discouraging in others AVID may be best for reducing power consumption AVID could be extended for further dynamic alteration of processors, limited reconfigurable computing AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Future Work Extension of AVID to throttle other possible components Further static removal of components Actual full SPEC benchmark comparisons of standard, DIVA, and AVID architectures Exploration of speculation in several ways, using AVID for verification and feedback AVID: Breaking Processors for Increased Performance & Reduced Power Consumption

Questions? You know you have them! Ask! Go on, pick us apart! AVID: Breaking Processors for Increased Performance & Reduced Power Consumption