libuuid: fix lib internal cache size

The lib internal cache improves throughput in high load
scenarios but for applications with a low request rate,
the cache size must be adapted to this situation.
Therefore the cache size should be changed to the current
requirements of the application during runtime.

diff --git a/libuuid/src/gen_uuid.c b/libuuid/src/gen_uuid.c
index e1ba3c3d0e993253a1059cc75ed822832b26c2ee..619ef0131378193a9ea573aa790514401ac49807 100644 (file)
--- a/libuuid/src/gen_uuid.c
+++ b/libuuid/src/gen_uuid.c
@@ -528,25 +528,35 @@ int __uuid_generate_time_cont(uuid_t out, int *num, uint32_t cont_offset)
  */
 static int uuid_generate_time_generic(uuid_t out) {
 #ifdef HAVE_TLS
+       /* thread local cache for uuidd based requests */
+       const int                       cs_min = (1<<6);
+       const int                       cs_max = (1<<18);
+       const int                       cs_factor = 2;
        THREAD_LOCAL int                num = 0;
-       THREAD_LOCAL int                cache_size = 1;
+       THREAD_LOCAL int                cache_size = cs_min;
+       THREAD_LOCAL int                last_used = 0;
        THREAD_LOCAL struct uuid        uu;
        THREAD_LOCAL time_t             last_time = 0;
        time_t                          now;
 
-       if (num > 0) {
+       if (num > 0) { /* expire cache */
                now = time(NULL);
-               if (now > last_time+1)
+               if (now > last_time+1) {
+                       last_used = cache_size - num;
                        num = 0;
+               }
        }
-       if (num <= 0) {
+       if (num <= 0) { /* fill cache */
                /*
                 * num + OP_BULK provides a local cache in each application.
                 * Start with a small cache size to cover short running applications
-                * and increment the cache size over the runntime.
+                * and adjust the cache size over the runntime.
                 */
-               if (cache_size < 1000000)
-                       cache_size *= 10;
+               if ((last_used == cache_size) && (cache_size < cs_max))
+                       cache_size *= cs_factor;
+               else if ((last_used < (cache_size / cs_factor)) && (cache_size > cs_min))
+                       cache_size /= cs_factor;
+
                num = cache_size;
 
                if (get_uuid_via_daemon(UUIDD_OP_BULK_TIME_UUID,
@@ -556,9 +566,11 @@ static int uuid_generate_time_generic(uuid_t out) {
                        num--;
                        return 0;
                }
+               /* request to daemon failed, reset cache */
                num = 0;
+               cache_size = cs_min;
        }
-       if (num > 0) {
+       if (num > 0) { /* serve uuid from cache */
                uu.time_low++;
                if (uu.time_low == 0) {
                        uu.time_mid++;
@@ -567,6 +579,8 @@ static int uuid_generate_time_generic(uuid_t out) {
                }
                num--;
                uuid_pack(&uu, out);
+               if (num == 0)
+                       last_used = cache_size;
                return 0;
        }
 #else