The following commit has been merged into the perf/core branch of tip: Commit-ID: 43358d9dfb250842383cddad816a7538548a5070 Gitweb: https://git.kernel.org/tip/43358d9dfb250842383cddad816a7538548a5070 Author: Adrian Hunter <adrian.hun...@intel.com> AuthorDate: Wed, 29 Apr 2020 18:07:50 +03:00 Committer: Arnaldo Carvalho de Melo <a...@redhat.com> CommitterDate: Tue, 05 May 2020 16:35:30 -03:00
perf intel-pt: Update documentation about itrace G and L options Provide a little more information about the new G and L options, particularly the issue with large PEBs. Signed-off-by: Adrian Hunter <adrian.hun...@intel.com> Cc: Andi Kleen <a...@linux.intel.com> Cc: Jiri Olsa <jo...@redhat.com> Link: http://lore.kernel.org/lkml/20200429150751.12570-9-adrian.hun...@intel.com Signed-off-by: Arnaldo Carvalho de Melo <a...@redhat.com> --- tools/perf/Documentation/itrace.txt | 4 ++- tools/perf/Documentation/perf-intel-pt.txt | 35 +++++++++++++++++++++- 2 files changed, 39 insertions(+) diff --git a/tools/perf/Documentation/itrace.txt b/tools/perf/Documentation/itrace.txt index 0326050..2714847 100644 --- a/tools/perf/Documentation/itrace.txt +++ b/tools/perf/Documentation/itrace.txt @@ -33,6 +33,10 @@ Also the number of last branch entries (default 64, max. 1024) for instructions or transactions events can be specified. + Similar to options g and l, size may also be specified for options G and L. + On x86, note that G and L work poorly when data has been recorded with + large PEBS. Refer linkperf:perf-intel-pt[1] man page for details. + It is also possible to skip events generated (instructions, branches, transactions, ptwrite, power) at the beginning. This is useful to ignore initialization code. diff --git a/tools/perf/Documentation/perf-intel-pt.txt b/tools/perf/Documentation/perf-intel-pt.txt index 456fdcb..782eb8a 100644 --- a/tools/perf/Documentation/perf-intel-pt.txt +++ b/tools/perf/Documentation/perf-intel-pt.txt @@ -821,7 +821,9 @@ The letters are: e synthesize tracing error events d create a debug log g synthesize a call chain (use with i or x) + G synthesize a call chain on existing event records l synthesize last branch entries (use with i or x) + L synthesize last branch entries on existing event records s skip initial number of events "Instructions" events look like they were recorded by "perf record -e @@ -912,6 +914,39 @@ transactions events can be specified. e.g. Note that last branch entries are cleared for each sample, so there is no overlap from one sample to the next. +The G and L options are designed in particular for sample mode, and work much +like g and l but add call chain and branch stack to the other selected events +instead of synthesized events. For example, to record branch-misses events for +'ls' and then add a call chain derived from the Intel PT trace: + + perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' -- ls + perf report --itrace=Ge + +Although in fact G is a default for perf report, so that is the same as just: + + perf report + +One caveat with the G and L options is that they work poorly with "Large PEBS". +Large PEBS means PEBS records will be accumulated by hardware and the written +into the event buffer in one go. That reduces interrupts, but can give very +late timestamps. Because the Intel PT trace is synchronized by timestamps, +the PEBS events do not match the trace. Currently, Large PEBS is used only in +certain circumstances: + - hardware supports it + - PEBS is used + - event period is specified, instead of frequency + - the sample type is limited to the following flags: + PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR | + PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_STREAM_ID | + PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER | + PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR | + PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_REGS_USER | + PERF_SAMPLE_PERIOD (and sometimes) | PERF_SAMPLE_TIME +Because Intel PT sample mode uses a different sample type to the list above, +Large PEBS is not used with Intel PT sample mode. To avoid Large PEBS in other +cases, avoid specifying the event period i.e. avoid the 'perf record' -c option, +--count option, or 'period' config term. + To disable trace decoding entirely, use the option --no-itrace. It is also possible to skip events generated (instructions, branches, transactions)
