linux-kernel - [PATCH] perf record: Synthesize cgroup events only if needed

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Date:   Fri, 27 Nov 2020 14:43:56 +0900
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>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH] perf record: Synthesize cgroup events only if needed

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

Fixes: 8fb4b67939e16 ("perf record: Add --all-cgroups option")
Signed-off-by: Namhyung Kim <namhyung@...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 8a23391558cf..d9c624377da7 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;
-- 
2.29.2.454.gaff20da3a2-goog