tools api fs: Cache cgroupfs mount point

Currently it parses the /proc file everytime it opens a file in the
cgroupfs.  Save the last result to avoid it (assuming it won't be
changed between the accesses).

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201216090556.813996-3-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/lib/api/fs/cgroup.c b/tools/lib/api/fs/cgroup.c
index 262a422..1573dae 100644 (file)
--- a/tools/lib/api/fs/cgroup.c
+++ b/tools/lib/api/fs/cgroup.c
@@ -8,6 +8,14 @@
 #include <string.h>
 #include "fs.h"
 
+struct cgroupfs_cache_entry {
+       char    subsys[32];
+       char    mountpoint[PATH_MAX];
+};
+
+/* just cache last used one */
+static struct cgroupfs_cache_entry cached;
+
 int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
 {
        FILE *fp;
@@ -16,6 +24,14 @@ int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
        char *p, *path;
        char mountpoint[PATH_MAX];
 
+       if (!strcmp(cached.subsys, subsys)) {
+               if (strlen(cached.mountpoint) < maxlen) {
+                       strcpy(buf, cached.mountpoint);
+                       return 0;
+               }
+               return -1;
+       }
+
        fp = fopen("/proc/mounts", "r");
        if (!fp)
                return -1;
@@ -75,6 +91,9 @@ int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
        free(line);
        fclose(fp);
 
+       strncpy(cached.subsys, subsys, sizeof(cached.subsys) - 1);
+       strcpy(cached.mountpoint, mountpoint);
+
        if (mountpoint[0] && strlen(mountpoint) < maxlen) {
                strcpy(buf, mountpoint);
                return 0;