linux-kernel - [PATCH] perf record: Fix wrong comm in system-wide mode with delay

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Date:   Fri, 27 Aug 2021 16:32:12 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Stephane Eranian <eranian@...gle.com>
Subject: [PATCH] perf record: Fix wrong comm in system-wide mode with delay

Stephane found that the name of the forked process in a system-wide
mode is wrong when --delay option is used.  For example,

  # perf record -a --delay=1000  noploop 3

The noploop process will run a busy loop for 3 second.  And on an idle
machine it should show up at the top in the perf report.  It works
well without the --delay option.  But if I add the option, it showed
'perf' not 'noploop'.

  # perf report -s comm -q | head -3
      52.94%  perf
      16.65%  swapper
      12.04%  chrome

It turned out that the dummy event didn't work at all and it missed
COMM and MMAP events for the noploop process (and others too).  We
should enable the dummy event immediately in system-wide mode, as the
enable-on-exec would work only for task events.

With this change,

  # perf report -s comm -q | head -3
      52.75%  noploop
      17.03%  swapper
      12.83%  chrome

Cc: Adrian Hunter <adrian.hunter@...el.com>
Reported-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/builtin-record.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 548c1dbde6c5..acfe66e31cf0 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -910,7 +910,8 @@ static int record__open(struct record *rec)
 		 * Enable the dummy event when the process is forked for
 		 * initial_delay, immediately for system wide.
 		 */
-		if (opts->initial_delay && !pos->immediate)
+		if (opts->initial_delay && !pos->immediate &&
+		    !target__has_cpu(&opts->target))
 			pos->core.attr.enable_on_exec = 1;
 		else
 			pos->immediate = 1;
-- 
2.33.0.259.gc128427fd7-goog