for #320, set socket send buffer to smaller macro. 2.0.131

@@ -1110,6 +1110,11 @@ void SrsRtmpConn::change_mw_sleep(int sleep_ms)
     // socket send buffer, system will double it.
     int nb_sbuf = socket_buffer_size / 2;
     
+    // override the send buffer by macro.
+    #ifdef SRS_PERF_SO_SNDBUF_SIZE
+    nb_sbuf = SRS_PERF_SO_SNDBUF_SIZE / 2;
+    #endif
+    
     // set the socket send buffer when required larger buffer
     if (setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &nb_sbuf, sock_buf_size) < 0) {
         srs_warn("set sock SO_SENDBUF=%d failed.", nb_sbuf);

@@ -31,7 +31,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 // current release version
 #define VERSION_MAJOR       2
 #define VERSION_MINOR       0
-#define VERSION_REVISION    130
+#define VERSION_REVISION    131
 
 // server info.
 #define RTMP_SIG_SRS_KEY "SRS"

@@ -169,6 +169,17 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 //#define SRS_PERF_TCP_NODELAY
 #undef SRS_PERF_TCP_NODELAY
+/**
+* set the socket send buffer,
+* to force the server to send smaller tcp packet.
+* @see https://github.com/winlinvip/simple-rtmp-server/issues/320
+* @remark undef it to auto calc it by merged write sleep ms.
+* @remark only apply it when SRS_PERF_MW_SO_RCVBUF is defined.
+*/
+#ifdef SRS_PERF_MW_SO_SNDBUF
+    //#define SRS_PERF_SO_SNDBUF_SIZE 1024
+    #undef SRS_PERF_SO_SNDBUF_SIZE
+#endif
 
 #endif
 

@@ -148,6 +148,24 @@ void show_macro_features()
     srs_trace("MW(merged-write) default sleep %d", SRS_PERF_MW_SLEEP);
     srs_trace("read chunk stream cache cid [0, %d)", SRS_PERF_CHUNK_STREAM_CACHE);
     srs_trace("default gop cache %d, play queue %ds", SRS_PERF_GOP_CACHE, SRS_PERF_PLAY_QUEUE);
+    
+#ifndef SRS_PERF_COMPLEX_SEND
+    srs_warn("complex send algorithm disabled.");
+#else
+    srs_trace("complex send algorithm enabled.");
+#endif
+
+#ifdef SRS_PERF_TCP_NODELAY
+    srs_warn("TCP_NODELAY enabled, hurts performance.");
+#else
+    srs_trace("TCP_NODELAY disabled.");
+#endif
+
+#ifdef SRS_PERF_SO_SNDBUF_SIZE
+    srs_warn("socket send buffer size %d", SRS_PERF_SO_SNDBUF_SIZE);
+#else
+    srs_trace("auto guess socket send buffer by merged write");
+#endif
 
     int possible_mr_latency = 0;
 #ifdef SRS_PERF_MERGED_READ
@@ -170,6 +188,10 @@ void check_macro_features()
     #warning "using develop SRS, please use release instead."
     srs_warn("SRS %s is develop branch, please use %s instead", RTMP_SIG_SRS_VERSION, RTMP_SIG_SRS_RELEASE);
 #endif
+
+#if defined(SRS_PERF_SO_SNDBUF_SIZE) && !defined(SRS_PERF_MW_SO_SNDBUF)
+    #error "SRS_PERF_SO_SNDBUF_SIZE depends on SRS_PERF_MW_SO_SNDBUF"
+#endif
 }
 
 /**