Why is RIOSend slower than classic winapi socket send? - sockets

Question

I am testing two apps with TCP sockets. First app uses new RIO socket calls, the second app uses classic Winsock socket calls. Both apps send a single string to a server. I made them both use non-blocking sockets and disabled the Nagle algorithm. When I measure the time it takes to execute the sends, contrary to my expectations the classic socket is faster. What is the reason for this?
Here is my code:
/*
Classic socket
*/
SOCKET ConnectSocket = INVALID_SOCKET;
// ... socket initialization
// Make socket non-blocking and disable Nagle's algorithm
unsigned long mode = 1;
ioctlsocket(ConnectSocket, FIONBIO, &mode);
int isOn = 1;
setsockopt(ConnectSocket, IPPROTO_TCP, TCP_NODELAY, (char *) &isOn, sizeof(int) );
// Measure exec time
t1 = __rdtscp(&dum);
iResult = send(ConnectSocket, sendbuf, (int)strlen(sendbuf), 0);
t2 = __rdtscp(&dum);
cout << (t2 - t1) / 3000.0f << " 10^-6 sec" << endl;
/*
RIO socket
*/
SOCKET s = WSASocket(
AF_INET,
SOCK_STREAM,
IPPROTO_TCP,
NULL,
0,
WSA_FLAG_REGISTERED_IO);
// ... socket initialization
// Make socket non-blocking and disable Nagel's algorithm
unsigned long mode = 1;
ioctlsocket(s, FIONBIO, &mode);
int isOn = 1;
setsockopt(s, IPPROTO_TCP, TCP_NODELAY, (char *)&isOn, sizeof(int));
// RIO socket is event-based
hEvent = WSACreateEvent();
RIO_NOTIFICATION_COMPLETION type;
type.Type = RIO_EVENT_COMPLETION;
type.Event.EventHandle = hEvent;
type.Event.NotifyReset = TRUE;
RIO_CQ complQueue = rioFuncTable.RIOCreateCompletionQueue(1000, &type);
RIO_RQ requestQueue = rioFuncTable.RIOCreateRequestQueue(
s,
10,
1,
10,
1,
complQueue,
complQueue,
NULL);
// Init rio buffers
char *pSndBuffer = new char[sndBufferSize + 1]();
std::copy(message, message + sndBufferSize, pSndBuffer); // put message to a server here
RIO_BUFFERID sndBufID = rioFuncTable.RIORegisterBuffer(pSndBuffer, sndBufferSize);
RIO_BUF sndBuffer;
sndBuffer.BufferId = sndBufID;
sndBuffer.Offset = 0;
sndBuffer.Length = sndBufferSize;
// Measure exec time
t1 = __rdtscp(&dum);
rioFuncTable.RIOSend(requestQueue, &sndBuffer, 1, 0, NULL);
t2 = __rdtscp(&dum);
cout << (t2 - t1) / 3000.0f << " 10^-6 sec" << endl;

Answer 1

RioSend() sends for real. send() memcopies the buffer to socket's tx buffer.