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diff --git a/docs/perf/performance-monitoring-unit.rst b/docs/perf/performance-monitoring-unit.rst new file mode 100644 index 0000000..5dd1af5 --- /dev/null +++ b/docs/perf/performance-monitoring-unit.rst @@ -0,0 +1,158 @@ +Performance Monitoring Unit +=========================== + +The Performance Monitoring Unit (PMU) allows recording of architectural and +microarchitectural events for profiling purposes. + +This document gives an overview of the PMU counter configuration to assist with +implementation and to complement the PMU security guidelines given in the +:ref:`Secure Development Guidelines` document. + +.. note:: + This section applies to Armv8-A implementations which have version 3 + of the Performance Monitors Extension (PMUv3). + +PMU Counters +------------ + +The PMU makes 32 counters available at all privilege levels: + +- 31 programmable event counters: ``PMEVCNTR<n>``, where ``n`` is ``0`` to + ``30``. +- A dedicated cycle counter: ``PMCCNTR``. + +Architectural mappings +~~~~~~~~~~~~~~~~~~~~~~ + ++--------------+---------+----------------------------+ +| Counters | State | System Register Name | ++==============+=========+============================+ +| | AArch64 | ``PMEVCNTR<n>_EL0[63*:0]`` | +| Programmable +---------+----------------------------+ +| | AArch32 | ``PMEVCNTR<n>[31:0]`` | ++--------------+---------+----------------------------+ +| | AArch64 | ``PMCCNTR_EL0[63:0]`` | +| Cycle +---------+----------------------------+ +| | AArch32 | ``PMCCNTR[63:0]`` | ++--------------+---------+----------------------------+ + +.. note:: + Bits [63:32] are only available if ARMv8.5-PMU is implemented. Refer to the + `Arm ARM`_ for a detailed description of ARMv8.5-PMU features. + +Configuring the PMU for counting events +--------------------------------------- + +Each programmable counter has an associated register, ``PMEVTYPER<n>`` which +configures it. The cycle counter has the ``PMCCFILTR_EL0`` register, which has +an identical function and bit field layout as ``PMEVTYPER<n>``. In addition, +the counters are enabled (permitted to increment) via the ``PMCNTENSET`` and +``PMCR`` registers. These can be accessed at all privilege levels. + +Architectural mappings +~~~~~~~~~~~~~~~~~~~~~~ + ++-----------------------------+------------------------+ +| AArch64 | AArch32 | ++=============================+========================+ +| ``PMEVTYPER<n>_EL0[63*:0]`` | ``PMEVTYPER<n>[31:0]`` | ++-----------------------------+------------------------+ +| ``PMCCFILTR_EL0[63*:0]`` | ``PMCCFILTR[31:0]`` | ++-----------------------------+------------------------+ +| ``PMCNTENSET_EL0[63*:0]`` | ``PMCNTENSET[31:0]`` | ++-----------------------------+------------------------+ +| ``PMCR_EL0[63*:0]`` | ``PMCR[31:0]`` | ++-----------------------------+------------------------+ + +.. note:: + Bits [63:32] are reserved. + +Relevant register fields +~~~~~~~~~~~~~~~~~~~~~~~~ + +For ``PMEVTYPER<n>_EL0``/``PMEVTYPER<n>`` and ``PMCCFILTR_EL0/PMCCFILTR``, the +most important fields are: + +- ``P``: + + - Bit 31. + - If set to ``0``, will increment the associated ``PMEVCNTR<n>`` at EL1. + +- ``NSK``: + + - Bit 29. + - If equal to the ``P`` bit it enables the associated ``PMEVCNTR<n>`` at + Non-secure EL1. + - Reserved if EL3 not implemented. + +- ``NSH``: + + - Bit 27. + - If set to ``1``, will increment the associated ``PMEVCNTR<n>`` at EL2. + - Reserved if EL2 not implemented. + +- ``SH``: + + - Bit 24. + - If different to the ``NSH`` bit it enables the associated ``PMEVCNTR<n>`` + at Secure EL2. + - Reserved if Secure EL2 not implemented. + +- ``M``: + + - Bit 26. + - If equal to the ``P`` bit it enables the associated ``PMEVCNTR<n>`` at + EL3. + +- ``evtCount[15:10]``: + + - Extension to ``evtCount[9:0]``. Reserved unless ARMv8.1-PMU implemented. + +- ``evtCount[9:0]``: + + - The event number that the associated ``PMEVCNTR<n>`` will count. + +For ``PMCNTENSET_EL0``/``PMCNTENSET``, the most important fields are: + +- ``P[30:0]``: + + - Setting bit ``P[n]`` to ``1`` enables counter ``PMEVCNTR<n>``. + - The effects of ``PMEVTYPER<n>`` are applied on top of this. + In other words, the counter will not increment at any privilege level or + security state unless it is enabled here. + +- ``C``: + + - Bit 31. + - If set to ``1`` enables the cycle counter ``PMCCNTR``. + +For ``PMCR``/``PMCR_EL0``, the most important fields are: + +- ``DP``: + + - Bit 5. + - If set to ``1`` it disables the cycle counter ``PMCCNTR`` where event + counting (by ``PMEVCNTR<n>``) is prohibited (e.g. EL2 and the Secure + world). + - If set to ``0``, ``PMCCNTR`` will not be affected by this bit and + therefore will be able to count where the programmable counters are + prohibited. + +- ``E``: + + - Bit 0. + - Enables/disables counting altogether. + - The effects of ``PMCNTENSET`` and ``PMCR.DP`` are applied on top of this. + In other words, if this bit is ``0`` then no counters will increment + regardless of how the other PMU system registers or bit fields are + configured. + +.. rubric:: References + +- `Arm ARM`_ + +-------------- + +*Copyright (c) 2019-2020, Arm Limited and Contributors. All rights reserved.* + +.. _Arm ARM: https://developer.arm.com/docs/ddi0487/latest |