Read and process as many packets as possible in read_udp_packets, to avoid having to run the entire event loop once per packet. (Patch from the Google tree.)

ares_process.c

@@ -399,13 +399,17 @@ static void read_udp_packets(ares_channel channel, fd_set *read_fds,
          * extra system calls and confusion. */
         FD_CLR(server->udp_socket, read_fds);
 
+      /* To reduce event loop overhead, read and process as many
+       * packets as we can. */
+      do {
         count = sread(server->udp_socket, buf, sizeof(buf));
         if (count == -1 && try_again(SOCKERRNO))
           continue;
         else if (count <= 0)
           handle_error(channel, i, now);
-
+        else
           process_answer(channel, buf, (int)count, i, 0, now);
+       } while (count > 0);
     }
 }