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

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@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201127054356.405481-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 8a23391..d9c6243 100644 (file)
--- 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;