docs/perf/psci-performance-instr.rst

4 TF-A provides two instrumentation tools for performing analysis of the PSCI
18 at runtime from the Performance Measurement Unit
21 measure hardware events. This means, for instance, that the PMU might be used to
24 TF-A utilises the PMF as a backend for the two instrumentation services it
27 instance, the PSCI Statistics service registers the PMF service
30 This is reserved a unique ID, name, and space in memory by the PMF. The
32 values from ``psci_svc`` at runtime.  Alternatively, the service may be
33 configured such that the PMF dumps those values to the console. A platform may
34 choose to expose SMCs that allow retrieval of these timestamps from the
37 This feature is enabled with the Boolean flag ``ENABLE_PMF``.
43 power states used by the platform. The service tracks residency time and
44 entry count. Residency time is the total time spent in a particular power
45 state by a PE. The entry count is the number of times the PE has entered
46 the power state. PSCI Statistics implements the optional functions
47 ``PSCI_STAT_RESIDENCY`` and ``PSCI_STAT_COUNT`` from the `PSCI`_
53     :param target_cpu: Contains copy of affinity fields in the MPIDR register
54       for identifying the target core (See section 5.1.4 of `PSCI`_
57       state. Generally, this parameter takes the same form as the power_state
61       and the highest level expressed in ``power_state``.
66     :param target_cpu: follows the same format as ``PSCI_STAT_RESIDENCY``.
67     :param power_state: follows the same format as ``PSCI_STAT_RESIDENCY``.
69     :returns: Number of times the state expressed in ``power_state`` has been
70       used by ``target_cpu`` and the highest level expressed in
74 and does this regardless of the entry mechanism into those states. The
77 PSCI Statistics is enabled with the Boolean build flag
78 ``ENABLE_PSCI_STAT``.  All Arm platforms utilise the PMF unless another
85 around the PMF to provide timestamp data. Although the service is not
86 restricted to PSCI, it is used primarily in TF-A to quantify the total time
87 spent in the PSCI implementation. The tool can be used to instrument other
88 components in TF-A as well. It is enabled with the Boolean flag
92 In PSCI, this service provides instrumentation points in the
95 * Entry into the PSCI SMC handler
96 * Exit from the PSCI SMC handler
102 The service captures the cycle count, which allows for the time spent in the
103 implementation to be calculated, given the frequency counter.
108 The timestamp during entry into the handler is captured as early as possible
109 during the runtime exception, prior to entry into the handler itself. All
111 captured after normal return from the PSCI SMC handler, or, if a low power state
112 was requested, it is captured in the warm boot path.