linux-kernel - [PATCH 5.9 138/152] perf record: Synthesize cgroup events only if needed

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Message-Id: <20201201084729.892592993@linuxfoundation.org>
Date:   Tue,  1 Dec 2020 09:54:13 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.9 138/152] perf record: Synthesize cgroup events only if needed

From: Namhyung Kim <namhyung@...nel.org>

[ Upstream commit aa50d953c169e876413bf237319e728dd41d9fdd ]

It didn't check the tool->cgroup_events bit which is set when the
--all-cgroups option is given.  Without it, samples will not have cgroup
info so no reason to synthesize.

We can check the PERF_RECORD_CGROUP records after running perf record
*WITHOUT* the --all-cgroups option:

Before:

  $ perf report -D | grep CGROUP
  0 0 0x8430 [0x38]: PERF_RECORD_CGROUP cgroup: 1 /
          CGROUP events:          1
          CGROUP events:          0
          CGROUP events:          0

After:

  $ perf report -D | grep CGROUP
          CGROUP events:          0
          CGROUP events:          0
          CGROUP events:          0

Committer testing:

Before:

  # perf record -a sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 2.208 MB perf.data (10003 samples) ]
  # perf report -D | grep "CGROUP events"
            CGROUP events:        146
            CGROUP events:          0
            CGROUP events:          0
  #

After:

  # perf record -a sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 2.208 MB perf.data (10448 samples) ]
  # perf report -D | grep "CGROUP events"
            CGROUP events:          0
            CGROUP events:          0
            CGROUP events:          0
  #

With all-cgroups:

  # perf record --all-cgroups -a sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 2.374 MB perf.data (11526 samples) ]
  # perf report -D | grep "CGROUP events"
            CGROUP events:        146
            CGROUP events:          0
            CGROUP events:          0
  #

Fixes: 8fb4b67939e16 ("perf record: Add --all-cgroups option")
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Acked-by: Jiri Olsa <jolsa@...hat.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Ian Rogers <irogers@...gle.com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Link: http://lore.kernel.org/lkml/20201127054356.405481-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/perf/util/synthetic-events.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 89b390623b63d..54ca751a2b3b3 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -563,6 +563,9 @@ int perf_event__synthesize_cgroups(struct perf_tool *tool,
 	char cgrp_root[PATH_MAX];
 	size_t mount_len;  /* length of mount point in the path */
 
+	if (!tool || !tool->cgroup_events)
+		return 0;
+
 	if (cgroupfs_find_mountpoint(cgrp_root, PATH_MAX, "perf_event") < 0) {
 		pr_debug("cannot find cgroup mount point\n");
 		return -1;
-- 
2.27.0