[tip:perf/core] perf tools: Use scandir() to replace readdir()

[tip-bot for Kan Liang]

Commit-ID:  ecdad24d7a4480c9af0ff6dbe00ac8bbae720d19
Gitweb:     http://git.kernel.org/tip/ecdad24d7a4480c9af0ff6dbe00ac8bbae720d19
Author:     Kan Liang <kan.liang@xxxxxxxxx>
AuthorDate: Thu, 7 Sep 2017 10:55:46 -0700
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Wed, 13 Sep 2017 09:49:15 -0300

perf tools: Use scandir() to replace readdir()

In perf_event__synthesize_threads() perf goes through all proc files
serially by readdir.

scandir() does a snapshoot of /proc, which is multithreading friendly.

It's possible that some threads which are added during event synthesize.
But the number of lost threads should be small.  They should not impact
the final analysis.

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Lukasz Odzioba <lukasz.odzioba@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1504806954-150842-3-git-send-email-kan.liang@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/event.c | 45 +++++++++++++++++++++++++--------------------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 1c905ba..17c21ea 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -683,12 +683,14 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
 				   bool mmap_data,
 				   unsigned int proc_map_timeout)
 {
-	DIR *proc;
-	char proc_path[PATH_MAX];
-	struct dirent *dirent;
 	union perf_event *comm_event, *mmap_event, *fork_event;
 	union perf_event *namespaces_event;
+	char proc_path[PATH_MAX];
+	struct dirent **dirent;
 	int err = -1;
+	char *end;
+	pid_t pid;
+	int n, i;
 
 	if (machine__is_default_guest(machine))
 		return 0;
@@ -712,29 +714,32 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
 		goto out_free_fork;
 
 	snprintf(proc_path, sizeof(proc_path), "%s/proc", machine->root_dir);
-	proc = opendir(proc_path);
+	n = scandir(proc_path, &dirent, 0, alphasort);
 
-	if (proc == NULL)
+	if (n < 0)
 		goto out_free_namespaces;
 
-	while ((dirent = readdir(proc)) != NULL) {
-		char *end;
-		pid_t pid = strtol(dirent->d_name, &end, 10);
-
-		if (*end) /* only interested in proper numerical dirents */
+	for (i = 0; i < n; i++) {
+		if (!isdigit(dirent[i]->d_name[0]))
 			continue;
-		/*
- 		 * We may race with exiting thread, so don't stop just because
- 		 * one thread couldn't be synthesized.
- 		 */
-		__event__synthesize_thread(comm_event, mmap_event, fork_event,
-					   namespaces_event, pid, 1, process,
-					   tool, machine, mmap_data,
-					   proc_map_timeout);
-	}
 
+		pid = (pid_t)strtol(dirent[i]->d_name, &end, 10);
+		/* only interested in proper numerical dirents */
+		if (!*end) {
+			/*
+			 * We may race with exiting thread, so don't stop just because
+			 * one thread couldn't be synthesized.
+			 */
+			__event__synthesize_thread(comm_event, mmap_event, fork_event,
+						   namespaces_event, pid, 1, process,
+						   tool, machine, mmap_data,
+						   proc_map_timeout);
+		}
+		free(dirent[i]);
+	}
+	free(dirent);
 	err = 0;
-	closedir(proc);
+
 out_free_namespaces:
 	free(namespaces_event);
 out_free_fork: