PAFLib is an IBM written library which exposes Power Architecture Facilities to userspace via an API. This includes the Data Stream Control Register Facility (DSCR) and the Event-Based Branching facility (EBB). Linux kernel 3.9 has exposed problem-state DSCR usage for ISA 2.06 (POWER7 – emulated) and ISA 2.07 (POWER8 – in hardware). Linux 3.10 has exposed the EBB facility.
Event Based Branching
To use the EBB library, just link to -lpaf-ebb. The system must be POWER ISA 2.07 compliant (POWER >= 8) to get EBB functionality.
The EBB library is automatically built when the compiler is able to generate instructions for POWER >= 8. In other words, when the compiler is using --with-cpu=power8. However, there are some cases in which the compiler doesn't generate POWER8 instructions by default, but the user wants to build the EBB library. In those cases, there are 2 options:
- Configure paflib with '--enable-ebb', which will force the build of EBB library.
- Configure paflib with CFLAGS='-mcpu=power8'.
It's important to notice that, in both cases the library won't execute on processors that don't implement the POWER ISA 2.07.
Data Stream Control Register
To use the DSCR library just link to -lpaf-dsc. The system must be POWER ISA 2.05 compliant (POWER6+) to get DSCR functionality and depending of the system supportted ISA the DSCR will operate in a different manner:
- Power ISA 2.05 (POWER6): SSE (Store Stream Enable) and DPFD (Default Prefetch Depth);
- Power ISA 2.06 (POWER7): SNSE (Stride-N Stream Enable);
- Power ISA 2.06+ (POWER7+): LSD (Load Stream Disable)
- Power ISA 2.07 (POWER8): URG (Depth Attainment Urgency), SWTE (Software Transient Enable), HWTE (Hardware Transient Enable), STE (Store Transient Enable), LTE (Load Transient Enable), SWUE (Software Unit Count Enable), HWUE (Hardware Unit Count Enable), and UNITCNT (Unit Count).
Also depending of the ISA the access to DSCR is privileged or not:
- Power ISA 2.05/2.06/2.06+: Privileged
- Power ISA 2.07: Problem-state (userland accessible).