New connections_above_limit() heuristic?

Author: ylavic

server/mpm/event/event.c

@@ -660,26 +660,31 @@ static int enable_listensocks(void)
     return 1;
 }
 
-static APR_INLINE apr_uint32_t listeners_disabled(void)
+static APR_INLINE int listeners_disabled(void)
 {
-    return apr_atomic_read32(&listensocks_disabled);
+    return apr_atomic_read32(&listensocks_disabled) != 0;
 }
 
-static APR_INLINE int connections_above_limit(int *busy)
+static APR_INLINE apr_uint32_t u32_min(apr_uint32_t u1, apr_uint32_t u2)
 {
-    apr_uint32_t i_count = ap_queue_info_num_idlers(worker_queue_info);
-    if (i_count > 0) {
-        apr_uint32_t c_count = apr_atomic_read32(&connection_count);
-        apr_uint32_t l_count = apr_atomic_read32(&lingering_count);
-        if (c_count <= l_count
-                /* Off by 'listeners_disabled()' to avoid flip flop */
-                || c_count - l_count < (apr_uint32_t)threads_per_child +
-                                       (i_count - listeners_disabled()) *
-                                       async_factor) {
+    return (u1 < u2) ? u1 : u2;
+}
+
+static int connections_above_limit(int *busy)
+{
+#ifndef LISTEN_OFF_RATE
+#define LISTEN_OFF_RATE 4u
+#endif
+    apr_uint32_t t_p_c = (apr_uint32_t)threads_per_child;
+    apr_uint32_t i_num = ap_queue_info_num_idlers(worker_queue_info);
+    apr_uint32_t i_min = listeners_disabled() ? t_p_c / LISTEN_OFF_RATE : 0;
+    if (i_num > i_min) { /* amortize disable=>enable_listensocks() switch */
+        apr_uint32_t t_num = t_p_c + i_num * async_factor;
+        if (apr_atomic_read32(pending_q->total) <= t_num) {
             return 0;
         }
     }
-    else if (busy) {
+    else if (busy && !i_num) {
         *busy = 1;
     }
     return 1;