diff --git a/trunk/src/app/srs_app_rtmp_conn.cpp b/trunk/src/app/srs_app_rtmp_conn.cpp
index acd302059..186760361 100644
--- a/trunk/src/app/srs_app_rtmp_conn.cpp
+++ b/trunk/src/app/srs_app_rtmp_conn.cpp
@@ -69,9 +69,6 @@ using namespace std;
 // when edge timeout, retry next.
 #define SRS_EDGE_TOKEN_TRAVERSE_TIMEOUT_US (int64_t)(3*1000*1000LL)
 
-// to get msgs then totally send out.
-#define SYS_MAX_PLAY_SEND_MSGS 128
-
 SrsRtmpConn::SrsRtmpConn(SrsServer* srs_server, st_netfd_t client_stfd)
     : SrsConnection(srs_server, client_stfd)
 {
@@ -520,7 +517,7 @@ int SrsRtmpConn::playing(SrsSource* source)
     
     // initialize other components
     SrsPithyPrint pithy_print(SRS_CONSTS_STAGE_PLAY_USER);
-    SrsSharedPtrMessageArray msgs(SYS_MAX_PLAY_SEND_MSGS);
+    SrsSharedPtrMessageArray msgs(SYS_CONSTS_MAX_PLAY_SEND_MSGS);
     bool user_specified_duration_to_stop = (req->duration > 0);
     int64_t starttime = -1;
     
diff --git a/trunk/src/app/srs_app_server.cpp b/trunk/src/app/srs_app_server.cpp
index 49df43998..d9ce8c389 100644
--- a/trunk/src/app/srs_app_server.cpp
+++ b/trunk/src/app/srs_app_server.cpp
@@ -50,12 +50,13 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #define SERVER_LISTEN_BACKLOG 512
 
-// system interval
+// system interval in ms,
 // all resolution times should be times togother,
 // for example, system-time is 3(300ms),
 // then rusage can be 3*x, for instance, 3*10=30(3s),
 // the meminfo canbe 30*x, for instance, 30*2=60(6s)
 // for performance refine, @see: https://github.com/winlinvip/simple-rtmp-server/issues/194
+// @remark, recomment to 1000ms.
 #define SRS_SYS_CYCLE_INTERVAL 1000
 
 // update time interval:
diff --git a/trunk/src/app/srs_app_source.cpp b/trunk/src/app/srs_app_source.cpp
index 64fd2d0e0..f25e64e3e 100644
--- a/trunk/src/app/srs_app_source.cpp
+++ b/trunk/src/app/srs_app_source.cpp
@@ -216,7 +216,7 @@ int SrsMessageQueue::dump_packets(int max_count, SrsSharedPtrMessage** pmsgs, in
     } else {
         // erase some vector elements may cause memory copy,
         // maybe can use more efficient vector.swap to avoid copy.
-        // @remark for the pmsgs is big enough, for instance, SYS_MAX_PLAY_SEND_MSGS 128,
+        // @remark for the pmsgs is big enough, for instance, SYS_CONSTS_MAX_PLAY_SEND_MSGS 128,
         //      the rtmp play client will get 128msgs once, so this branch rarely execute.
         msgs.erase(msgs.begin(), msgs.begin() + count);
     }
diff --git a/trunk/src/kernel/srs_kernel_consts.hpp b/trunk/src/kernel/srs_kernel_consts.hpp
index 4bb551311..d30fd07d1 100644
--- a/trunk/src/kernel/srs_kernel_consts.hpp
+++ b/trunk/src/kernel/srs_kernel_consts.hpp
@@ -78,6 +78,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 // the timeout to wait for client control message,
 // if timeout, we generally ignore and send the data to client,
 // generally, it's the pulse time for data seding.
+// @remark, recomment to 500ms.
 #define SRS_CONSTS_RTMP_PULSE_TIMEOUT_US (int64_t)(500*1000LL)
 
 /**
@@ -97,18 +98,42 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 // always use fmt0 as cache.
 //#define SRS_CONSTS_RTMP_MAX_FMT3_HEADER_SIZE 5
 
+/**
+* how many msgs can be send entirely.
+* for play clients to get msgs then totally send out.
+* for example, 25fps video, 40ms per video packet, 
+* while audio is 20ms per audio packet where 2/3 is audios,
+* when SYS_CONSTS_MAX_PLAY_SEND_MSGS is 128, then
+* we will send all 128*40ms/3=1706ms packets in a time,
+* which should greater than the SRS_CONSTS_RTMP_PULSE_TIMEOUT_US
+* (for example, 500ms), that is, we should:
+*       SYS_CONSTS_MAX_PLAY_SEND_MSGS * 40 / 3 >= SRS_CONSTS_RTMP_PULSE_TIMEOUT_US
+* @remark, recomment to 128.
+*/
+#define SYS_CONSTS_MAX_PLAY_SEND_MSGS 128
 /**
 * for performance issue, 
 * the iovs cache, @see https://github.com/winlinvip/simple-rtmp-server/issues/194
 * iovs cache for multiple messages for each connections.
+* each iovc is 16bytes, sizeof(iovec)=16, suppose the chunk size is 64k,
+* each message send in a chunk which needs only 2 iovec,
+* so the iovs max should be (SYS_CONSTS_MAX_PLAY_SEND_MSGS * 16 * 2)
+*
+* @remark, SRS will realloc when the iovs not enough.
 */
-#define SRS_CONSTS_IOVS_MAX 1024
+#define SRS_CONSTS_IOVS_MAX (SYS_CONSTS_MAX_PLAY_SEND_MSGS * 32)
 /**
 * for performance issue, 
 * the c0c3 cache, @see https://github.com/winlinvip/simple-rtmp-server/issues/194
 * c0c3 cache for multiple messages for each connections.
+* each c0 <= 16byes, suppose the chunk size is 64k,
+* each message send in a chunk which needs only a c0 header,
+* so the c0c3 cache should be (SYS_CONSTS_MAX_PLAY_SEND_MSGS * 16)
+*
+* @remark, SRS will try another loop when c0c3 cache dry, for we cannot realloc it.
+*       so we use larger c0c3 cache, that is (SYS_CONSTS_MAX_PLAY_SEND_MSGS * 32)
 */
-#define SRS_CONSTS_C0C3_HEADERS_MAX 4096
+#define SRS_CONSTS_C0C3_HEADERS_MAX (SYS_CONSTS_MAX_PLAY_SEND_MSGS * 32)
 
 ///////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////
diff --git a/trunk/src/rtmp/srs_protocol_rtmp.hpp b/trunk/src/rtmp/srs_protocol_rtmp.hpp
index e6dcb0b51..70fc8e8ca 100644
--- a/trunk/src/rtmp/srs_protocol_rtmp.hpp
+++ b/trunk/src/rtmp/srs_protocol_rtmp.hpp
@@ -374,6 +374,9 @@ public:
     * @param msgs, the msgs to send out, never be NULL.
     * @param nb_msgs, the size of msgs to send out.
     * @param stream_id, the stream id of packet to send over, 0 for control message.
+    *
+    * @remark performance issue, to support 6k+ 250kbps client,
+    *       @see https://github.com/winlinvip/simple-rtmp-server/issues/194
     */
     virtual int send_and_free_messages(SrsSharedPtrMessage** msgs, int nb_msgs, int stream_id);
     /**