perf record: Disable buildid cache options by default in switch output mode

The cost of buildid cache processing is high: reading all events in
output perf.data, opening each elf file to read buildids then copying
them into ~/.debug directory. In switch output mode, these heavy works
block perf from receiving 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>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1461178794-40467-6-git-send-email-wangnan0@huawei.com
Signed-off-by: He Kuang <hekuang@huawei.com>
[ Updated man page ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 30 insertions, 2 deletions

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 79a8a14f37b1..8dbee832abd9 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -358,7 +358,7 @@ A possible use case is to, given an external event, slice the perf.data file
 that gets then processed, possibly via a perf script, to decide if that
 particular perf.data snapshot should be kept or not.
 
-Implies --timestamp-filename.
+Implies --timestamp-filename, --no-buildid and --no-buildid-cache.
 
 SEE ALSO
 --------
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 80b805b7f5c7..178b49ecd05f 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1387,8 +1387,36 @@ 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) {