pmc-rs provides a safe abstraction for interacting with Performance Monitor Counters on [FreeBSD].

PMCs are part of the CPU hardware and are typically used to profile CPU micro-architecture events such as L1/L2/etc cache hit ratio, instructions processed per CPU tick, TLB lookups, branch mispredictions, etc for a particular application or algorithm. Using PMCs an algorithm can be tuned for performance by minimising CPU stalls, optimising CPU cache usage, etc.

The events are defined by the CPU manufacturer (here is the Intel 64 and IA-32 Architectures Developer's Manual: vol. 3B where the events can be found in section 18.2.1.2 "Pre-defined Architectural Performance Events", Table 18-1 "UMask and Event Select Encodings for Pre-Defined Architectural Performance Events").

pmc-rs makes use of the [libpmc] userland interace to the [hwpmc] kernel module on [FreeBSD].

Future improvements

• Support sampling PMCs.
• Read counters with the RDPMC instruction to avoid context switching.
• Split Counter into ProcessCounter and SystemCounter to enforce invariants specific to each scope using the type system.