Performance Data Standard and API Shirley Browne, Jack Dongarra, and Philip Mucci University of Tennessee from the Ptools Annual Meeting, May 1998

Performance Counters Almost all high performance processors include hardware performance counters. Most platforms APIs, if they exist, are not appropriate, functional or well documented. Existing performance counter APIs –Cray T3E –SGI MIPS R10000 –IBM Power series –DEC Alpha pfm pseudo-device interface –Windows 95, NT and Linux

Goals Specify a standard application interface (API) for accessing hardware performance counters Include a standard set of definitions for a common set of performance metrics To encourage vendors to implement the standard API for their platforms based on the reference implementation

Issues Ease of use and interpretation Availability of counters and restrictions on the number that can be measured at once Differentiating between the system, the user’s process and other processes Guarding against counter overflow Handling dynamic/speculative execution

Intended Users Performance Tool Developers Application engineers needing performance data to evaluate, model and tune their applications SIP CHSSI team leader (ARL MSRC) has requested cross-platform access to performance counters

Performance Data A common set of performance metrics. Target information that most affects how applications are tuned (exact set to be determined with help of user input)

Performance Data (cont.) –I/D cache misses for different levels –Branch mispredictions –TLB misses –Pipeline stalls due to memory subsystem –Pipeline stalls due to resource conflicts –Cache invalidations –TLB invalidations –Load/store count –Instruction count –Cycle count –Floating point instruction count –Integer instruction count –Branch taken / not taken count

Reference Implementations Reference implementations of the API have been discussed for the following pending funding and support: –Sun Ultra –MIPS R10000 –POWER architecture –Pentium family –Cray T3E Will be layered over the best existing vendor-specific APIs for these platforms

Results Portable performance tools on every platform No longer will developers have to rely on prof as the lowest common denominator of tools.