[igt-dev] [PATCH igt 2/2] lib: Cache the debugfs mountpoint

[Chris Wilson]

When using igt_debugfs_*() inside a tight loop, the overhead of calling
xstat64 (from is_mountpoint()) creeps up in the profiles. Eliminate it
by caching the resultant path for finding/mounting debugfs.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 lib/igt_debugfs.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/lib/igt_debugfs.c b/lib/igt_debugfs.c
index 4a119985..09d42ea0 100644
--- a/lib/igt_debugfs.c
+++ b/lib/igt_debugfs.c
@@ -110,6 +110,20 @@ static bool is_mountpoint(const char *path)
 	return dev != st.st_dev;
 }
 
+static const char *__igt_debugfs_mount(void)
+{
+	if (is_mountpoint("/sys/kernel/debug"))
+		return "/sys/kernel/debug";
+
+	if (is_mountpoint("/debug"))
+		return "/debug";
+
+	if (mount("debug", "/sys/kernel/debug", "debugfs", 0, 0))
+		return NULL;
+
+	return "/sys/kernel/debug";
+}
+
 /**
  * igt_debugfs_mount:
  *
@@ -121,16 +135,12 @@ static bool is_mountpoint(const char *path)
  */
 const char *igt_debugfs_mount(void)
 {
-	if (is_mountpoint("/sys/kernel/debug"))
-		return "/sys/kernel/debug";
+	static const char *path;
 
-	if (is_mountpoint("/debug"))
-		return "/debug";
+	if (!path)
+		path = __igt_debugfs_mount();
 
-	if (mount("debug", "/sys/kernel/debug", "debugfs", 0, 0))
-		return NULL;
-
-	return "/sys/kernel/debug";
+	return path;
 }
 
 /**
-- 
2.16.1