perf tools: Add documentation for perf.data on disk format
Add some documentation for the on disk format of perf.data. This is not documenting the actual perf events -- which are documented in perf_event.h -- but just the additional headers that perf record adds around them when writing the data to disk. Signed-off-by: Andi Kleen <ak@linux.intel.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Jiri Olsa <jolsa@kernel.org> Link: http://lkml.kernel.org/r/1466800885-12974-1-git-send-email-andi@firstfloor.org Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Andi Kleen
Arnaldo Carvalho de Melo
parent
d905768c9e
commit
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perf.data format
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Uptodate as of v4.7
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This document describes the on-disk perf.data format, generated by perf record
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or perf inject and consumed by the other perf tools.
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On a high level perf.data contains the events generated by the PMUs, plus metadata.
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All fields are in native-endian of the machine that generated the perf.data.
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When perf is writing to a pipe it uses a special version of the file
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format that does not rely on seeking to adjust data offsets. This
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format is not described here. The pipe version can be converted to
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normal perf.data with perf inject.
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The file starts with a perf_header:
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struct perf_header {
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char magic[8]; /* PERFILE2 */
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uint64_t size; /* size of the header */
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uint64_t attr_size; /* size of an attribute in attrs */
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struct perf_file_section attrs;
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struct perf_file_section data;
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struct perf_file_section event_types;
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uint64_t flags;
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uint64_t flags1[3];
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};
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The magic number identifies the perf file and the version. Current perf versions
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use PERFILE2. Old perf versions generated a version 1 format (PERFFILE). Version 1
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is not described here. The magic number also identifies the endian. When the
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magic value is 64bit byte swapped compared the file is in non-native
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endian.
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A perf_file_section contains a pointer to another section of the perf file.
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The header contains three such pointers: for attributes, data and event types.
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struct perf_file_section {
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uint64_t offset; /* offset from start of file */
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uint64_t size; /* size of the section */
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};
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Flags section:
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The header is followed by different optional headers, described by the bits set
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in flags. Only headers for which the bit is set are included. Each header
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consists of a perf_file_section located after the initial header.
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The respective perf_file_section points to the data of the additional
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header and defines its size.
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Some headers consist of strings, which are defined like this:
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struct perf_header_string {
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uint32_t len;
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char string[len]; /* zero terminated */
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};
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Some headers consist of a sequence of strings, which start with a
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struct perf_header_string_list {
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uint32_t nr;
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struct perf_header_string strings[nr]; /* variable length records */
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};
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The bits are the flags bits in a 256 bit bitmap starting with
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flags. These define the valid bits:
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HEADER_RESERVED = 0, /* always cleared */
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HEADER_FIRST_FEATURE = 1,
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HEADER_TRACING_DATA = 1,
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Describe me.
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HEADER_BUILD_ID = 2,
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The header consists of an sequence of build_id_event. The size of each record
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is defined by header.size (see perf_event.h). Each event defines a ELF build id
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for a executable file name for a pid. An ELF build id is a unique identifier
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assigned by the linker to an executable.
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struct build_id_event {
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struct perf_event_header header;
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pid_t pid;
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uint8_t build_id[24];
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char filename[header.size - offsetof(struct build_id_event, filename)];
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};
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HEADER_HOSTNAME = 3,
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A perf_header_string with the hostname where the data was collected
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(uname -n)
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HEADER_OSRELEASE = 4,
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A perf_header_string with the os release where the data was collected
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(uname -r)
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HEADER_VERSION = 5,
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A perf_header_string with the perf user tool version where the
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data was collected. This is the same as the version of the source tree
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the perf tool was built from.
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HEADER_ARCH = 6,
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A perf_header_string with the CPU architecture (uname -m)
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HEADER_NRCPUS = 7,
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A structure defining the number of CPUs.
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struct nr_cpus {
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uint32_t nr_cpus_online;
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uint32_t nr_cpus_available; /* CPUs not yet onlined */
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};
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HEADER_CPUDESC = 8,
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A perf_header_string with description of the CPU. On x86 this is the model name
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in /proc/cpuinfo
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HEADER_CPUID = 9,
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A perf_header_string with the exact CPU type. On x86 this is
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vendor,family,model,stepping. For example: GenuineIntel,6,69,1
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HEADER_TOTAL_MEM = 10,
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An uint64_t with the total memory in bytes.
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HEADER_CMDLINE = 11,
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A perf_header_string with the perf command line used to collect the data.
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HEADER_EVENT_DESC = 12,
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Another description of the perf_event_attrs, more detailed than header.attrs
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including IDs and names. See perf_event.h or the man page for a description
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of a struct perf_event_attr.
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struct {
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uint32_t nr; /* number of events */
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uint32_t attr_size; /* size of each perf_event_attr */
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struct {
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struct perf_event_attr attr; /* size of attr_size */
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uint32_t nr_ids;
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struct perf_header_string event_string;
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uint64_t ids[nr_ids];
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} events[nr]; /* Variable length records */
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};
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HEADER_CPU_TOPOLOGY = 13,
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String lists defining the core and CPU threads topology.
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struct {
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struct perf_header_string_list cores; /* Variable length */
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struct perf_header_string_list threads; /* Variable length */
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};
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Example:
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sibling cores : 0-3
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sibling threads : 0-1
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sibling threads : 2-3
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HEADER_NUMA_TOPOLOGY = 14,
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A list of NUMA node descriptions
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struct {
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uint32_t nr;
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struct {
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uint32_t nodenr;
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uint64_t mem_total;
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uint64_t mem_free;
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struct perf_header_string cpus;
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} nodes[nr]; /* Variable length records */
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};
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HEADER_BRANCH_STACK = 15,
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Not implemented in perf.
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HEADER_PMU_MAPPINGS = 16,
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A list of PMU structures, defining the different PMUs supported by perf.
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struct {
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uint32_t nr;
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struct pmu {
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uint32_t pmu_type;
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struct perf_header_string pmu_name;
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} [nr]; /* Variable length records */
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};
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HEADER_GROUP_DESC = 17,
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Description of counter groups ({...} in perf syntax)
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struct {
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uint32_t nr;
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struct {
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struct perf_header_string string;
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uint32_t leader_idx;
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uint32_t nr_members;
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} [nr]; /* Variable length records */
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};
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HEADER_AUXTRACE = 18,
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Define additional auxtrace areas in the perf.data. auxtrace is used to store
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undecoded hardware tracing information, such as Intel Processor Trace data.
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/**
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* struct auxtrace_index_entry - indexes a AUX area tracing event within a
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* perf.data file.
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* @file_offset: offset within the perf.data file
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* @sz: size of the event
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*/
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struct auxtrace_index_entry {
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u64 file_offset;
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u64 sz;
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};
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#define PERF_AUXTRACE_INDEX_ENTRY_COUNT 256
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/**
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* struct auxtrace_index - index of AUX area tracing events within a perf.data
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* file.
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* @list: linking a number of arrays of entries
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* @nr: number of entries
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* @entries: array of entries
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*/
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struct auxtrace_index {
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struct list_head list;
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size_t nr;
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struct auxtrace_index_entry entries[PERF_AUXTRACE_INDEX_ENTRY_COUNT];
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};
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other bits are reserved and should ignored for now
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HEADER_FEAT_BITS = 256,
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Attributes
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This is an array of perf_event_attrs, each attr_size bytes long, which defines
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each event collected. See perf_event.h or the man page for a detailed
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description.
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Data
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This section is the bulk of the file. It consist of a stream of perf_events
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describing events. This matches the format generated by the kernel.
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See perf_event.h or the manpage for a detailed description.
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Some notes on parsing:
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Ordering
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The events are not necessarily in time stamp order, as they can be
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collected in parallel on different CPUs. If the events should be
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processed in time order they need to be sorted first. It is possible
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to only do a partial sort using the FINISHED_ROUND event header (see
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below). perf record guarantees that there is no reordering over a
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FINISHED_ROUND.
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ID vs IDENTIFIER
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When the event stream contains multiple events each event is identified
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by an ID. This can be either through the PERF_SAMPLE_ID or the
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PERF_SAMPLE_IDENTIFIER header. The PERF_SAMPLE_IDENTIFIER header is
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at a fixed offset from the event header, which allows reliable
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parsing of the header. Relying on ID may be ambigious.
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IDENTIFIER is only supported by newer Linux kernels.
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Perf record specific events:
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In addition to the kernel generated event types perf record adds its
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own event types (in addition it also synthesizes some kernel events,
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for example MMAP events)
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PERF_RECORD_USER_TYPE_START = 64,
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PERF_RECORD_HEADER_ATTR = 64,
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struct attr_event {
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struct perf_event_header header;
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struct perf_event_attr attr;
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uint64_t id[];
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};
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PERF_RECORD_HEADER_EVENT_TYPE = 65, /* depreceated */
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#define MAX_EVENT_NAME 64
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struct perf_trace_event_type {
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uint64_t event_id;
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char name[MAX_EVENT_NAME];
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};
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struct event_type_event {
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struct perf_event_header header;
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struct perf_trace_event_type event_type;
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};
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PERF_RECORD_HEADER_TRACING_DATA = 66,
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Describe me
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struct tracing_data_event {
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struct perf_event_header header;
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uint32_t size;
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};
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PERF_RECORD_HEADER_BUILD_ID = 67,
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Define a ELF build ID for a referenced executable.
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struct build_id_event; /* See above */
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PERF_RECORD_FINISHED_ROUND = 68,
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No event reordering over this header. No payload.
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PERF_RECORD_ID_INDEX = 69,
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Map event ids to CPUs and TIDs.
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struct id_index_entry {
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uint64_t id;
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uint64_t idx;
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uint64_t cpu;
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uint64_t tid;
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};
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struct id_index_event {
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struct perf_event_header header;
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uint64_t nr;
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struct id_index_entry entries[nr];
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};
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PERF_RECORD_AUXTRACE_INFO = 70,
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Auxtrace type specific information. Describe me
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struct auxtrace_info_event {
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struct perf_event_header header;
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uint32_t type;
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uint32_t reserved__; /* For alignment */
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uint64_t priv[];
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};
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PERF_RECORD_AUXTRACE = 71,
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Defines auxtrace data. Followed by the actual data. The contents of
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the auxtrace data is dependent on the event and the CPU. For example
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for Intel Processor Trace it contains Processor Trace data generated
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by the CPU.
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struct auxtrace_event {
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struct perf_event_header header;
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uint64_t size;
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uint64_t offset;
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uint64_t reference;
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uint32_t idx;
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uint32_t tid;
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uint32_t cpu;
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uint32_t reserved__; /* For alignment */
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};
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struct aux_event {
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struct perf_event_header header;
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uint64_t aux_offset;
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uint64_t aux_size;
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uint64_t flags;
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};
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PERF_RECORD_AUXTRACE_ERROR = 72,
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Describes an error in hardware tracing
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enum auxtrace_error_type {
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PERF_AUXTRACE_ERROR_ITRACE = 1,
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PERF_AUXTRACE_ERROR_MAX
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};
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#define MAX_AUXTRACE_ERROR_MSG 64
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struct auxtrace_error_event {
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struct perf_event_header header;
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uint32_t type;
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uint32_t code;
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uint32_t cpu;
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uint32_t pid;
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uint32_t tid;
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uint32_t reserved__; /* For alignment */
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uint64_t ip;
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char msg[MAX_AUXTRACE_ERROR_MSG];
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};
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Event types
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Define the event attributes with their IDs.
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An array bound by the perf_file_section size.
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struct {
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struct perf_event_attr attr; /* Size defined by header.attr_size */
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struct perf_file_section ids;
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}
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ids points to a array of uint64_t defining the ids for event attr attr.
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References:
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include/uapi/linux/perf_event.h
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This is the canonical description of the kernel generated perf_events
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and the perf_event_attrs.
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perf_events manpage
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A manpage describing perf_event and perf_event_attr is here:
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http://web.eece.maine.edu/~vweaver/projects/perf_events/programming.html
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This tends to be slightly behind the kernel include, but has better
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descriptions. An (typically older) version of the man page may be
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included with the standard Linux man pages, available with "man
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perf_events"
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pmu-tools
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https://github.com/andikleen/pmu-tools/tree/master/parser
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A definition of the perf.data format in python "construct" format is available
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in pmu-tools parser. This allows to read perf.data from python and dump it.
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quipper
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The quipper C++ parser is available at
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https://chromium.googlesource.com/chromiumos/platform/chromiumos-wide-profiling/
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Unfortunately this parser tends to be many versions behind and may not be able
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to parse data files generated by recent perf.
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