Perf: Replace rtl_tcp linked list with ring buffer

Removed the linked list structure, locking, and malloc/free on each USB callback.
Replaced it with a non blocking ring buffer for performance.  This resulted
in a large performance improvement when using an Raspberry Pi or Raspberry Pi Zero W
as a rtl_tcp server.  The sample rate could be doubled and instead of wired ethernet
wifi could be used.  Frequnecy change lag was reduced greatly also.

Signed-off-by: Stephen Blinick <stephen@stesoft.com>

src/rtl_tcp.c

@@ -61,15 +61,8 @@ static pthread_t command_thread;
 static pthread_cond_t exit_cond;
 static pthread_mutex_t exit_cond_lock;
 
-static pthread_mutex_t ll_mutex;
 static pthread_cond_t cond;
 
-struct llist {
-	char *data;
-	size_t len;
-	struct llist *next;
-};
-
 typedef struct { /* structure size must be multiple of 2 bytes */
 	char magic[4];
 	uint32_t tuner_type;
@@ -79,9 +72,17 @@ typedef struct { /* structure size must be multiple of 2 bytes */
 static rtlsdr_dev_t *dev = NULL;
 
 static int enable_biastee = 0;
-static int global_numq = 0;
+
-static struct llist *ll_buffers = 0;
+// Ring Buffer declarations
-static int llbuf_num = 500;
+// 8MB appears to cover several seconds at high bitrates -- about as much lag as you'd want
+#define RINGBUFSZ_INIT (8*1024*1024)
+static int ringbuf_sz = RINGBUFSZ_INIT;
+static int ringbuf_trimsz = 512*1024;
+static unsigned char *ringbuf = NULL;
+static volatile unsigned int ringbuf_head = 0;
+static volatile unsigned int ringbuf_tail = 0;
+static unsigned int total_radio_bytes = 0;
+static unsigned int max_bytes_in_flight = 0;
 
 static volatile int do_exit = 0;
 
@@ -145,53 +146,60 @@ static void sighandler(int signum)
 
 void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx)
 {
-	if(!do_exit) {
+    static time_t lasttime = 0;
-		struct llist *rpt = (struct llist*)malloc(sizeof(struct llist));
+	static int lastbytes = 0;
-		rpt->data = (char*)malloc(len);
+	time_t curtime;
-		memcpy(rpt->data, buf, len);
-		rpt->len = len;
-		rpt->next = NULL;
 
-		pthread_mutex_lock(&ll_mutex);
+	if(!do_exit) {
-
+		unsigned int bufferleft;
-		if (ll_buffers == NULL) {
-			ll_buffers = rpt;
-		} else {
-			struct llist *cur = ll_buffers;
-			int num_queued = 0;
 
-			while (cur->next != NULL) {
+		if (ringbuf == NULL)
-				cur = cur->next;
+		{
-				num_queued++;
+			printf("Allocate %d bytes for ringbuf.\n", ringbuf_sz);
+			ringbuf = (unsigned char*)malloc(ringbuf_sz);
 		}
 
-			if(llbuf_num && llbuf_num == num_queued-2){
+		bufferleft = ringbuf_sz - ((ringbuf_head < ringbuf_tail) ? (ringbuf_head - ringbuf_tail + ringbuf_sz) : (ringbuf_head - ringbuf_tail));
-				struct llist *curelem;
+		if (len < bufferleft)
-
+		{
-				free(ll_buffers->data);
+			if ((ringbuf_head+len) < (unsigned int)ringbuf_sz)
-				curelem = ll_buffers->next;
+			{
-				free(ll_buffers);
+				memcpy(((unsigned char*)(ringbuf+ringbuf_head)), buf, len);
-				ll_buffers = curelem;
+			}
+			else
+			{
+				memcpy(((unsigned char*)ringbuf+ringbuf_head), buf, ringbuf_sz-ringbuf_head);
+				memcpy((unsigned char*)ringbuf, buf+(ringbuf_sz-ringbuf_head), len-(ringbuf_sz-ringbuf_head));
+			}
+			ringbuf_head = (ringbuf_head + len) % ringbuf_sz;
+		}
+		else
+		{
+			printf("overrun: head=%d tail=%d, Trimming %d bytes from tail of buffer\n", ringbuf_head, ringbuf_tail, ringbuf_trimsz);
+			ringbuf_tail = (ringbuf_tail + ringbuf_trimsz) % ringbuf_sz;
 		}
 
-			cur->next = rpt;
+		total_radio_bytes += len;
-
+		curtime = time (NULL);
-			if (num_queued > global_numq)
+		if ((curtime - lasttime) > 30)
-				printf("ll+, now %d\n", num_queued);
+		{
-			else if (num_queued < global_numq)
+		   int nsecs = curtime - lasttime;
-				printf("ll-, now %d\n", num_queued);
+		   int nbytes = total_radio_bytes - lastbytes;
-
+		   int bytes_in_flight = (ringbuf_head - ringbuf_tail);
-			global_numq = num_queued;
+		   if (bytes_in_flight < 0)
+			  bytes_in_flight = ringbuf_sz + bytes_in_flight;
+		   lasttime=curtime;
+		   lastbytes=total_radio_bytes;
+		   printf(">> [ %3.2fMB/s ]  [ bytes_in_flight(cur/max) = %4dK / %4dK ]\n",
+			  (float)nbytes/(float)nsecs/1000.0/1000.0, bytes_in_flight/1024, max_bytes_in_flight/1024);
+		   max_bytes_in_flight=0;
 		}
-		pthread_cond_signal(&cond);
-		pthread_mutex_unlock(&ll_mutex);
 	}
 }
 
 static void *tcp_worker(void *arg)
 {
-	struct llist *curelem,*prev;
+	int bytesleft, bytessent;
-	int bytesleft,bytessent, index;
 	struct timeval tv= {1,0};
 	struct timespec ts;
 	struct timeval tp;
@@ -202,36 +210,27 @@ static void *tcp_worker(void *arg)
 		if(do_exit)
 			pthread_exit(0);
 
-		pthread_mutex_lock(&ll_mutex);
+		bytesleft = (ringbuf_head < ringbuf_tail) ?
-		gettimeofday(&tp, NULL);
+		            (ringbuf_head - ringbuf_tail + ringbuf_sz) :
-		ts.tv_sec  = tp.tv_sec+5;
+					(ringbuf_head - ringbuf_tail);
-		ts.tv_nsec = tp.tv_usec * 1000;
+		while (bytesleft > 0)
-		r = pthread_cond_timedwait(&cond, &ll_mutex, &ts);
+		{
-		if(r == ETIMEDOUT) {
-			pthread_mutex_unlock(&ll_mutex);
-			printf("worker cond timeout\n");
-			sighandler(0);
-			pthread_exit(NULL);
-		}
-
-		curelem = ll_buffers;
-		ll_buffers = 0;
-		pthread_mutex_unlock(&ll_mutex);
-
-		while(curelem != 0) {
-			bytesleft = curelem->len;
-			index = 0;
-			bytessent = 0;
-			while(bytesleft > 0) {
 		   FD_ZERO(&writefds);
 		   FD_SET(s, &writefds);
 		   tv.tv_sec = 1;
 		   tv.tv_usec = 0;
 		   r = select(s+1, NULL, &writefds, NULL, &tv);
 		   if(r) {
-					bytessent = send(s,  &curelem->data[index], bytesleft, 0);
+			  unsigned int sendchunk;
+			  if (ringbuf_tail < ringbuf_head)
+				 sendchunk = ringbuf_head - ringbuf_tail;
+			  else
+				 sendchunk = ringbuf_sz - ringbuf_tail;
+			  if (sendchunk > max_bytes_in_flight)
+				 max_bytes_in_flight = sendchunk;
+			  bytessent = send(s,  (unsigned char*)(ringbuf+ringbuf_tail), sendchunk, 0);
 			  bytesleft -= bytessent;
-					index += bytessent;
+			  ringbuf_tail = (ringbuf_tail + bytessent) % ringbuf_sz;
 		   }
 		   if(bytessent == SOCKET_ERROR || do_exit) {
 			  printf("worker socket bye\n");
@@ -239,11 +238,6 @@ static void *tcp_worker(void *arg)
 			  pthread_exit(NULL);
 		   }
 		}
-			prev = curelem;
-			curelem = curelem->next;
-			free(prev->data);
-			free(prev);
-		}
 	}
 }
 
@@ -397,7 +391,7 @@ int main(int argc, char **argv)
 	struct sigaction sigact, sigign;
 #endif
 
-	while ((opt = getopt(argc, argv, "a:p:f:g:s:b:n:d:P:T")) != -1) {
+	while ((opt = getopt(argc, argv, "a:p:f:g:s:b:d:P:T")) != -1) {
 		switch (opt) {
 		case 'd':
 			dev_index = verbose_device_search(optarg);
@@ -421,9 +415,6 @@ int main(int argc, char **argv)
 		case 'b':
 			buf_num = atoi(optarg);
 			break;
-		case 'n':
-			llbuf_num = atoi(optarg);
-			break;
 		case 'P':
 			ppm_error = atoi(optarg);
 			break;
@@ -510,7 +501,6 @@ int main(int argc, char **argv)
 		fprintf(stderr, "WARNING: Failed to reset buffers.\n");
 
 	pthread_mutex_init(&exit_cond_lock, NULL);
-	pthread_mutex_init(&ll_mutex, NULL);
 	pthread_mutex_init(&exit_cond_lock, NULL);
 	pthread_cond_init(&cond, NULL);
 	pthread_cond_init(&exit_cond, NULL);
@@ -590,24 +580,16 @@ int main(int argc, char **argv)
 		closesocket(s);
 
 		printf("all threads dead..\n");
-		curelem = ll_buffers;
-		ll_buffers = 0;
-
-		while(curelem != 0) {
-			prev = curelem;
-			curelem = curelem->next;
-			free(prev->data);
-			free(prev);
-		}
 
 		do_exit = 0;
-		global_numq = 0;
 	}
 
 out:
 	rtlsdr_close(dev);
 	closesocket(listensocket);
 	closesocket(s);
+	if (ringbuf)
+	   free(ringbuf);
 #ifdef _WIN32
 	WSACleanup();
 #endif