linux-kernel - [PATCH RFC V2 02/10] perf tools: using scandir to replace readdir

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Date:   Sun, 10 Sep 2017 19:23:15 -0700
From:   kan.liang@...el.com
To:     acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     jolsa@...nel.org, namhyung@...nel.org, adrian.hunter@...el.com,
        lukasz.odzioba@...el.com, ak@...ux.intel.com,
        Kan Liang <kan.liang@...el.com>
Subject: [PATCH RFC V2 02/10] perf tools: using scandir to replace readdir

From: Kan Liang <kan.liang@...el.com>

For perf_event__synthesize_threads, perf goes through all proc files
serially by readdir.
scandir did 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@...el.com>
---
 tools/perf/util/event.c | 46 ++++++++++++++++++++++++++--------------------
 1 file changed, 26 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 1c905ba..c31f678 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 +714,33 @@ 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:
-- 
2.5.5