linux-kernel - [PATCH] perf record: add dummy event during system wide synthesis

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Message-Id: <20200416004713.192740-1-irogers@google.com>
Date:   Wed, 15 Apr 2020 17:47:13 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Cc:     Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH] perf record: add dummy event during system wide synthesis

During the processing of /proc during event synthesis new processes may
start. Add a dummy event if /proc is to be processed, to capture mmaps
for starting processes. This reuses the existing logic for
initial-delay.

Suggested-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/builtin-record.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 1ab349abe904..bab4fc8568d1 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -805,16 +805,18 @@ static int record__open(struct record *rec)
 	int rc = 0;
 
 	/*
-	 * For initial_delay we need to add a dummy event so that we can track
-	 * PERF_RECORD_MMAP while we wait for the initial delay to enable the
-	 * real events, the ones asked by the user.
+	 * For initial_delay or system wide, we need to add a dummy event so
+	 * that we can track PERF_RECORD_MMAP to cover the delay (of waiting or
+	 * synthesis) prior to the real user events being enabled.
 	 */
-	if (opts->initial_delay) {
+	if (opts->initial_delay || target__has_cpu(&opts->target)) {
 		if (perf_evlist__add_dummy(evlist))
 			return -ENOMEM;
 
+		/* Disable tracking of mmaps on lead event. */
 		pos = evlist__first(evlist);
 		pos->tracking = 0;
+		/* Activate dummy event immediately. */
 		pos = evlist__last(evlist);
 		pos->tracking = 1;
 		pos->core.attr.enable_on_exec = 1;
-- 
2.26.0.110.g2183baf09c-goog