Events

Events are occurrences of specific signals related to a processor’s function. Hardware performance counters exist as a small set of registers that count events, such as cache misses and floating point operations while the program executes on the processor. Other performance counters might exist on the operating system level for events such as page faults and context switches.

Monitoring these events facilitates correlation between the structure of source/object code and the efficiency of the mapping of that code to the underlying architecture. Each processor/architecture/system has a number of events that are native to it. PAPI provides a software abstraction of these architecture-dependent native events into a collection of preset events that are accessible through the PAPI interface.

PAPI.jl uses the Event type to represent both native events (PAPI.Native) and preset events (PAPI.Preset).

Native events

Native events comprise the set of all events that are countable by the system. In many cases, these events will be available through a matching preset PAPI event. These native events can also be access directly, however this usage is intended for people who are very familiar with the particular platform in use. PAPI provides access to native events on all supported platforms through the low-level interface.

Presets

The PAPI library provides approximately 100 presets (predefined events) that are a common set of events relevant for application performance tuning. These events are typically found in many processors that provide performance counters and give access to the memory hierarchy, cache coherence protocol events, cycle and instruction counts, functional unit, and pipeline status.

Preset events map symbolic names to specific native events on the particular architecture in use. For example, Total Cycles is represented as PAPI.TOT_CYC. A preset can be either directly available as a single counter, derived using a combination of counters, or unavailable on any particular platform.

A full list of the presets and their job description can be found here.

PAPI.jl includes the same set of presets represented as PAPI.TOT_CYC instead of PAPI_TOT_CYC.

The exact semantics of an event counter are platform dependent. PAPI preset names are mapped onto available events in a way, so it can count as many similar types of events as possible on different platforms. Due to hardware implementation differences, it is not necessarily feasible to directly compare the counts of a particular PAPI event obtained on different hardware platforms.

To determine which preset events are available on your specific platform, the available_presets function can be used:

available_presets()

(PAPI.L1_DCM, PAPI.L1_ICM, PAPI.L2_DCM, PAPI.L2_ICM, PAPI.L1_TCM, PAPI.L2_TCM, PAPI.L3_TCM, PAPI.CA_SNP, PAPI.CA_SHR, PAPI.CA_CLN, PAPI.CA_ITV, PAPI.L3_LDM, PAPI.TLB_DM, PAPI.TLB_IM, PAPI.L1_LDM, PAPI.L1_STM, PAPI.L2_LDM, PAPI.L2_STM, PAPI.PRF_DM, PAPI.MEM_WCY, PAPI.STL_ICY, PAPI.FUL_ICY, PAPI.STL_CCY, PAPI.FUL_CCY, PAPI.BR_UCN, PAPI.BR_CN, PAPI.BR_TKN, PAPI.BR_NTK, PAPI.BR_MSP, PAPI.BR_PRC, PAPI.TOT_INS, PAPI.LD_INS, PAPI.SR_INS, PAPI.BR_INS, PAPI.RES_STL, PAPI.TOT_CYC, PAPI.LST_INS, PAPI.L2_DCA, PAPI.L3_DCA, PAPI.L2_DCR, PAPI.L3_DCR, PAPI.L2_DCW, PAPI.L3_DCW, PAPI.L2_ICH, PAPI.L2_ICA, PAPI.L3_ICA, PAPI.L2_ICR, PAPI.L3_ICR, PAPI.L2_TCA, PAPI.L3_TCA, PAPI.L2_TCR, PAPI.L3_TCR, PAPI.L2_TCW, PAPI.L3_TCW, PAPI.SP_OPS, PAPI.DP_OPS, PAPI.VEC_SP, PAPI.VEC_DP, PAPI.REF_CYC)

The exists function tests whether a single native or preset event is available:

exists(PAPI.TOT_INS)

true

Accessing events

Preset events can be accessed using the predefined constants PAPI.TOT_CYC. All events can be accessed by name using the function name_to_event and converted back to their name with event_to_name

using PAPI #hide
tot_ins = name_to_event("PAPI_TOT_INS") # Total Instructions preset same as PAPI.TOT_INS
page_faults = name_to_event("PAGE-FAULTS") # Page-fault counter provided by perf, if available
tot_cyc = event"PAPI_TOT_CYC" # same, but with macro

Base.show automatically converts the event back to its corresponding name.

Available events

A full list of available events is provided by available_presets and available_native for presets and native events respectively.

available_presets()

available_native()