[PATCH 26/46] perf record: Disable buildid cache options by default in switch output mode

Wang Nan
2016-02-26T09:33:58Z

Cost of buildid cache processing is high: read all events in output
perf.data, open elf files to read buildid then copy them into
~/.debug directory. In switch output mode, causes perf stop receiving
from perf events for too long.

Enable no-buildid and no-buildid-cache by default if --switch-output
is provided. Still allow user use --no-no-buildid to explicitly enable
buildid in this case.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
tools/perf/builtin-record.c | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 0092e54..8a1523f 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1377,8 +1377,36 @@ int cmd_record(int argc, const char **argv, const char *prefix __maybe_unused)
"If some relocation was applied (e.g. kexec) symbols may be misresolved\n"
"even with a suitable vmlinux or kallsyms file.\n\n");

- if (rec->no_buildid_cache || rec->no_buildid)
+ if (rec->no_buildid_cache || rec->no_buildid) {
disable_buildid_cache();
+ } else if (rec->switch_output) {
+ /*
+ * In 'perf record --switch-output', disable buildid
+ * generation by default to reduce data file switching
+ * overhead. Still generate buildid if they are required
+ * explicitly using
+ *
+ * perf record --signal-trigger --no-no-buildid \
+ * --no-no-buildid-cache
+ *
+ * Following code equals to:
+ *
+ * if ((rec->no_buildid || !rec->no_buildid_set) &&
+ * (rec->no_buildid_cache || !rec->no_buildid_cache_set))
+ * disable_buildid_cache();
+ */
+ bool disable = true;
+
+ if (rec->no_buildid_set && !rec->no_buildid)
+ disable = false;
+ if (rec->no_buildid_cache_set && !rec->no_buildid_cache)
+ disable = false;
+ if (disable) {
+ rec->no_buildid = true;
+ rec->no_buildid_cache = true;
+ disable_buildid_cache();
+ }
+ }

if (rec->evlist->nr_entries == 0 &&
perf_evlist__add_default(rec->evlist) < 0) {
--
1.8.3.4