loop in output callback for performance.

diff --git a/dnstap/dtstream.c b/dnstap/dtstream.c
index 963d4769f7d9353f87dc9aa30b29a9872c2659a9..164b5692772deda9b711076a46440e0dc655edb6 100644 (file)
--- a/dnstap/dtstream.c
+++ b/dnstap/dtstream.c
@@ -50,6 +50,9 @@
 #include <sys/un.h>
 #endif
 
+/** number of messages to process in one output callback */
+#define DTIO_MESSAGES_PER_CALLBACK 100
+
 void* fstrm_create_control_frame_start(char* contenttype, size_t* len)
 {
        uint32_t* control;
@@ -591,30 +594,40 @@ static int dtio_check_close(struct dt_io_thread* dtio)
 static void dtio_output_cb(int ATTR_UNUSED(fd), short bits, void* arg)
 {
        struct dt_io_thread* dtio = (struct dt_io_thread*)arg;
+       int i;
 
        if((bits&UB_EV_READ)) {
                if(!dtio_check_close(dtio))
                        return;
        }
 
-       /* see if there are messages that need writing */
-       if(!dtio->cur_msg) {
-               if(!dtio_find_msg(dtio))
-                       return; /* nothing to do */
-       }
+       /* loop to process a number of messages.  This improves throughput,
+        * because selecting on write-event if not needed for busy messages
+        * (dnstap log) generation and if they need to all be written back.
+        * The write event is usually not blocked up.  But not forever,
+        * because the event loop needs to stay responsive for other events.
+        * If there are no (more) messages, or if the output buffers get
+        * full, it returns out of the loop. */
+       for(i=0; i<DTIO_MESSAGES_PER_CALLBACK; i++) {
+               /* see if there are messages that need writing */
+               if(!dtio->cur_msg) {
+                       if(!dtio_find_msg(dtio))
+                               return; /* nothing to do */
+               }
 
-       /* write it */
-       if(dtio->cur_msg_done < dtio->cur_msg_len) {
-               if(!dtio_write_more(dtio))
-                       return;
-       }
+               /* write it */
+               if(dtio->cur_msg_done < dtio->cur_msg_len) {
+                       if(!dtio_write_more(dtio))
+                               return;
+               }
 
-       /* done with the current message */
-       free(dtio->cur_msg);
-       dtio->cur_msg = NULL;
-       dtio->cur_msg_len = 0;
-       dtio->cur_msg_done = 0;
-       dtio->cur_msg_len_done = 0;
+               /* done with the current message */
+               free(dtio->cur_msg);
+               dtio->cur_msg = NULL;
+               dtio->cur_msg_len = 0;
+               dtio->cur_msg_done = 0;
+               dtio->cur_msg_len_done = 0;
+       }
 }
 
 /** callback for the dnstap commandpipe, to stop the dnstap IO */