From: Krzysztof Łopatowski <krzysztof.m.lopatowski@gmail.com>
Date: Thu, 6 Feb 2025 11:33:15 +0000 (+0100)
Subject: perf tools: Improve startup time by reducing unnecessary stat() calls
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=4bac7fb5862740087825eda3ed6168e91da8b7e6;p=users%2Fwilly%2Fxarray.git

perf tools: Improve startup time by reducing unnecessary stat() calls

When testing perf trace on NixOS, I noticed significant startup delays:
- `ls`: ~2ms
- `strace ls`: ~10ms
- `perf trace ls`: ~550ms

Profiling showed that 51% of the time is spent reading files,
26% in loading BPF programs, and 11% in `newfstatat`.

This patch optimizes module path exploration by avoiding `stat()` calls
unless necessary. For filesystems that do not implement `d_type`
(DT_UNKNOWN), it falls back to the old behavior.
See `readdir(3)` for details.

This reduces `perf trace ls` time to ~500ms.

A more thorough startup optimization based on command parameters would
be ideal, but that is a larger effort.

Signed-off-by: Krzysztof Łopatowski <krzysztof.m.lopatowski@gmail.com>
Acked-by: Howard Chu <howardchu95@gmail.com>
Link: https://lore.kernel.org/r/20250206113314.335376-2-krzysztof.m.lopatowski@gmail.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index d96cbfd97ad8..316f0879e5e0 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1339,7 +1339,7 @@ static int maps__set_module_path(struct maps *maps, const char *path, struct kmo
 
 static int maps__set_modules_path_dir(struct maps *maps, const char *dir_name, int depth)
 {
-	struct dirent *dent;
+	const struct dirent *dent;
 	DIR *dir = opendir(dir_name);
 	int ret = 0;
 
@@ -1350,14 +1350,20 @@ static int maps__set_modules_path_dir(struct maps *maps, const char *dir_name, i
 
 	while ((dent = readdir(dir)) != NULL) {
 		char path[PATH_MAX];
-		struct stat st;
+		unsigned char d_type = dent->d_type;
 
-		/*sshfs might return bad dent->d_type, so we have to stat*/
 		path__join(path, sizeof(path), dir_name, dent->d_name);
-		if (stat(path, &st))
-			continue;
 
-		if (S_ISDIR(st.st_mode)) {
+		if (d_type == DT_UNKNOWN) {
+			struct stat st;
+
+			if (stat(path, &st))
+				continue;
+			if (S_ISDIR(st.st_mode))
+				d_type = DT_DIR;
+		}
+
+		if (d_type == DT_DIR) {
 			if (!strcmp(dent->d_name, ".") ||
 			    !strcmp(dent->d_name, ".."))
 				continue;