diff options
| -rw-r--r-- | tools/perf/Documentation/perf-intel-pt.txt | 30 | ||||
| -rw-r--r-- | tools/perf/util/auxtrace.c | 3 | ||||
| -rw-r--r-- | tools/perf/util/intel-pt.c | 6 |
3 files changed, 39 insertions, 0 deletions
diff --git a/tools/perf/Documentation/perf-intel-pt.txt b/tools/perf/Documentation/perf-intel-pt.txt index 7b6ccd2fa3bf..9d485a9cdb19 100644 --- a/tools/perf/Documentation/perf-intel-pt.txt +++ b/tools/perf/Documentation/perf-intel-pt.txt @@ -1821,6 +1821,36 @@ Can be compiled and traced: $ +Pipe mode +--------- +Pipe mode is a problem for Intel PT and possibly other auxtrace users. +It's not recommended to use a pipe as data output with Intel PT because +of the following reason. + +Essentially the auxtrace buffers do not behave like the regular perf +event buffers. That is because the head and tail are updated by +software, but in the auxtrace case the data is written by hardware. +So the head and tail do not get updated as data is written. + +In the Intel PT case, the head and tail are updated only when the trace +is disabled by software, for example: + - full-trace, system wide : when buffer passes watermark + - full-trace, not system-wide : when buffer passes watermark or + context switches + - snapshot mode : as above but also when a snapshot is made + - sample mode : as above but also when a sample is made + +That means finished-round ordering doesn't work. An auxtrace buffer +can turn up that has data that extends back in time, possibly to the +very beginning of tracing. + +For a perf.data file, that problem is solved by going through the trace +and queuing up the auxtrace buffers in advance. + +For pipe mode, the order of events and timestamps can presumably +be messed up. + + EXAMPLE ------- diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c index c2e323cd7d49..d4b04fa07a11 100644 --- a/tools/perf/util/auxtrace.c +++ b/tools/perf/util/auxtrace.c @@ -1133,6 +1133,9 @@ int auxtrace_queue_data(struct perf_session *session, bool samples, bool events) if (auxtrace__dont_decode(session)) return 0; + if (perf_data__is_pipe(session->data)) + return 0; + if (!session->auxtrace || !session->auxtrace->queue_data) return -EINVAL; diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c index 6d3921627e33..b8b29756fbf1 100644 --- a/tools/perf/util/intel-pt.c +++ b/tools/perf/util/intel-pt.c @@ -4379,6 +4379,12 @@ int intel_pt_process_auxtrace_info(union perf_event *event, intel_pt_setup_pebs_events(pt); + if (perf_data__is_pipe(session->data)) { + pr_warning("WARNING: Intel PT with pipe mode is not recommended.\n" + " The output cannot relied upon. In particular,\n" + " timestamps and the order of events may be incorrect.\n"); + } + if (pt->sampling_mode || list_empty(&session->auxtrace_index)) err = auxtrace_queue_data(session, true, true); else |