поддержка Intel Processor Trace в инструментах perf (Support for Intel Processor Trace within perf tools)
Описание (Description)
Intel Processor Trace (Intel PT) is an extension of Intel
Architecture that collects information about software execution
such as control flow, execution modes and timings and formats it
into highly compressed binary packets. Technical details are
documented in the Intel 64 and IA-32 Architectures Software
Developer Manuals, Chapter 36 Intel Processor Trace.
Intel PT is first supported in Intel Core M and 5th generation
Intel Core processors that are based on the Intel
micro-architecture code name Broadwell.
Trace data is collected by perf record and stored within the
perf.data file. See below for options to perf record.
Trace data must be decoded which involves walking the object code
and matching the trace data packets. For example a TNT packet
only tells whether a conditional branch was taken or not taken,
so to make use of that packet the decoder must know precisely
which instruction was being executed.
Decoding is done on-the-fly. The decoder outputs samples in the
same format as samples output by perf hardware events, for
example as though the "instructions" or "branches" events had
been recorded. Presently 3 tools support this: perf script, perf
report and perf inject. See below for more information on using
those tools.
The main distinguishing feature of Intel PT is that the decoder
can determine the exact flow of software execution. Intel PT can
be used to understand why and how did software get to a certain
point, or behave a certain way. The software does not have to be
recompiled, so Intel PT works with debug or release builds,
however the executed images are needed - which makes use in
JIT-compiled environments, or with self-modified code, a
challenge. Also symbols need to be provided to make sense of
addresses.
A limitation of Intel PT is that it produces huge amounts of
trace data (hundreds of megabytes per second per core) which
takes a long time to decode, for example two or three orders of
magnitude longer than it took to collect. Another limitation is
the performance impact of tracing, something that will vary
depending on the use-case and architecture.
