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The contents of this directory allow users to specify PMU events in their
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CPUs by their symbolic names rather than raw event codes (see example below).
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The main program in this directory, is the 'jevents', which is built and
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executed _BEFORE_ the perf binary itself is built.
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The 'jevents' program tries to locate and process JSON files in the directory
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tree tools/perf/pmu-events/arch/foo.
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- Regular files with '.json' extension in the name are assumed to be
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JSON files, each of which describes a set of PMU events.
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- The CSV file that maps a specific CPU to its set of PMU events is to
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be named 'mapfile.csv' (see below for mapfile format).
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- Directories are traversed, but all other files are ignored.
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- To reduce JSON event duplication per architecture, platform JSONs may
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use "ArchStdEvent" keyword to dereference an "Architecture standard
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events", defined in architecture standard JSONs.
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Architecture standard JSONs must be located in the architecture root
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folder. Matching is based on the "EventName" field.
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The PMU events supported by a CPU model are expected to grouped into topics
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such as Pipelining, Cache, Memory, Floating-point etc. All events for a topic
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should be placed in a separate JSON file - where the file name identifies
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the topic. Eg: "Floating-point.json".
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All the topic JSON files for a CPU model/family should be in a separate
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sub directory. Thus for the Silvermont X86 CPU:
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$ ls tools/perf/pmu-events/arch/x86/Silvermont_core
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Cache.json Memory.json Virtual-Memory.json
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Frontend.json Pipeline.json
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The JSONs folder for a CPU model/family may be placed in the root arch
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folder, or may be placed in a vendor sub-folder under the arch folder
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for instances where the arch and vendor are not the same.
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Using the JSON files and the mapfile, 'jevents' generates the C source file,
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'pmu-events.c', which encodes the two sets of tables:
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- Set of 'PMU events tables' for all known CPUs in the architecture,
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(one table like the following, per JSON file; table name 'pme_power8'
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is derived from JSON file name, 'power8.json').
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struct pmu_event pme_power8[] = {
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...
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{
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.name = "pm_1plus_ppc_cmpl",
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.event = "event=0x100f2",
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.desc = "1 or more ppc insts finished,",
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},
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...
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}
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- A 'mapping table' that maps each CPU of the architecture, to its
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'PMU events table'
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struct pmu_events_map pmu_events_map[] = {
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{
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.cpuid = "004b0000",
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.version = "1",
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.type = "core",
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.table = pme_power8
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},
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...
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};
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After the 'pmu-events.c' is generated, it is compiled and the resulting
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'pmu-events.o' is added to 'libperf.a' which is then used to build perf.
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NOTES:
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1. Several CPUs can support same set of events and hence use a common
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JSON file. Hence several entries in the pmu_events_map[] could map
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to a single 'PMU events table'.
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2. The 'pmu-events.h' has an extern declaration for the mapping table
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and the generated 'pmu-events.c' defines this table.
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3. _All_ known CPU tables for architecture are included in the perf
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binary.
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At run time, perf determines the actual CPU it is running on, finds the
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matching events table and builds aliases for those events. This allows
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users to specify events by their name:
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$ perf stat -e pm_1plus_ppc_cmpl sleep 1
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where 'pm_1plus_ppc_cmpl' is a Power8 PMU event.
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However some errors in processing may cause the perf build to fail.
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Mapfile format
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===============
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The mapfile enables multiple CPU models to share a single set of PMU events.
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It is required even if such mapping is 1:1.
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The mapfile.csv format is expected to be:
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Header line
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CPUID,Version,Dir/path/name,Type
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where:
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Comma:
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is the required field delimiter (i.e other fields cannot
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have commas within them).
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Comments:
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Lines in which the first character is either '\n' or '#'
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are ignored.
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Header line
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The header line is the first line in the file, which is
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always _IGNORED_. It can empty.
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CPUID:
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CPUID is an arch-specific char string, that can be used
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to identify CPU (and associate it with a set of PMU events
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it supports). Multiple CPUIDS can point to the same
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File/path/name.json.
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Example:
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CPUID == 'GenuineIntel-6-2E' (on x86).
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CPUID == '004b0100' (PVR value in Powerpc)
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Version:
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is the Version of the mapfile.
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Dir/path/name:
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is the pathname to the directory containing the CPU's JSON
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files, relative to the directory containing the mapfile.csv
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Type:
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indicates whether the events or "core" or "uncore" events.
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Eg:
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$ grep Silvermont tools/perf/pmu-events/arch/x86/mapfile.csv
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GenuineIntel-6-37,V13,Silvermont_core,core
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GenuineIntel-6-4D,V13,Silvermont_core,core
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GenuineIntel-6-4C,V13,Silvermont_core,core
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i.e the three CPU models use the JSON files (i.e PMU events) listed
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in the directory 'tools/perf/pmu-events/arch/x86/Silvermont_core'.
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