[PATCH] perf data: Increase RLIMIT_NOFILE limit when open too many files in perf_data__create_dir()

[Yang Jihong]

If using parallel threads to collect data, perf record needs at least 6 fds
per CPU. (one for sys_perf_event_open, four for pipe msg and ack of the
pipe, see record__thread_data_open_pipes(), and one for open perf.data.XXX)
For an environment with more than 100 cores, if perf record uses both
`-a` and `--threads` options, it is easy to exceed the upper limit of the
file descriptor number, when we run out of them try to increase the limits.

Before:
  $ ulimit -n
  1024
  $ lscpu | grep 'On-line CPU(s)'
  On-line CPU(s) list:                0-159
  $ perf record --threads -a sleep 1
  Failed to create data directory: Too many open files

After:
  $ ulimit -n
  1024
  $ lscpu | grep 'On-line CPU(s)'
  On-line CPU(s) list:                0-159
  $ perf record --threads -a sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.394 MB perf.data (1576 samples) ]
Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
---
 tools/perf/util/data.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
index fc16299c915f..098f9e3bb2e7 100644
--- a/tools/perf/util/data.c
+++ b/tools/perf/util/data.c
@@ -17,6 +17,7 @@
 #include "util.h" // rm_rf_perf_data()
 #include "debug.h"
 #include "header.h"
+#include "evsel.h"
 #include <internal/lib.h>
 
 static void close_dir(struct perf_data_file *files, int nr)
@@ -35,6 +36,7 @@ void perf_data__close_dir(struct perf_data *data)
 
 int perf_data__create_dir(struct perf_data *data, int nr)
 {
+	enum rlimit_action set_rlimit = NO_CHANGE;
 	struct perf_data_file *files = NULL;
 	int i, ret;
 
@@ -54,11 +56,21 @@ int perf_data__create_dir(struct perf_data *data, int nr)
 			goto out_err;
 		}
 
+retry_open:
 		ret = open(file->path, O_RDWR|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR);
 		if (ret < 0) {
+			/*
+			 * If using parallel threads to collect data,
+			 * perf record needs at least 6 fds per CPU.
+			 * When we run out of them try to increase the limits.
+			 */
+			if (errno == EMFILE && evsel__increase_rlimit(&set_rlimit))
+				goto retry_open;
+
 			ret = -errno;
 			goto out_err;
 		}
+		set_rlimit = NO_CHANGE;
 
 		file->fd = ret;
 	}
-- 
2.34.1