Windows TCP socket recv delay - windows

Question

External controller sends 120-bytes message through TCP/IP socket every 30ms.
Application receives this messages through standard tcp/ip socket recv function.
It works perfectly under Linux & OSX (recv returns 120-bytes messages every 30ms).
Under Windows recv returns ~3500 bytes buffer about every 1 sec. Rest of time it returns 0.
Wireshark under Windows shows messages indeed coming every 30ms.
How to make windows tcp socket work properly (without delay) ?
PS: I've played with TCP_NODELAY & TcpAckFrequency already. Wireshark shows everything is ok. So I think it's some Windows optimization, that should be turned off.
Reading--
int WMaster::DataRead(void)
{
if (!open_ok) return 0;
if (!CheckSocket())
{
PrintErrNo();
return 0;
}
iResult = recv(ConnectSocket, (char *)input_buff,sizeof(input_buff),0);
nError=WSAGetLastError();
if(nError==0) return iResult;
if(nError==WSAEWOULDBLOCK) return iResult;
PrintErrNo();
return 0;
}
Initialization-
ConnectSocket = INVALID_SOCKET;
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
ZeroMemory(&clientService, sizeof(clientService));
clientService.sin_family = AF_INET;
clientService.sin_addr.s_addr = inet_addr( deviceName.toLatin1().constData() );
clientService.sin_port = htons( port);
iResult = setsockopt(ConnectSocket, IPPROTO_TCP, TCP_NODELAY, (char *) &flag,
sizeof (int));
u_long iMode=1;
iResult=ioctlsocket(ConnectSocket,FIONBIO,&iMode);
iResult = ::connect( ConnectSocket, (SOCKADDR*) &clientService,
sizeof(clientService) );
CheckSocket -
bool WMaster::CheckSocket(void)
{
socklen_t len = sizeof (int);
int retval = getsockopt (ConnectSocket, SOL_SOCKET, SO_ERROR, (char*)(&valopt), &len );
if (retval!=0)
{
open_ok=false;
return false;
};
return true;
}

Answer 1

Consider disabling the Nagle algorithm. 120-bytes is quite small and its possible that data is being buffered before being sent. Another reason I think it is the Nagle Algorithm is that about 33 sends should happen in 1 second. That corresponds with 33*120 = 3960 bytes / sec very similar to the 3500 you are seeing.

Answer 2

Change your dataread function as follows such that WSAGetLastError is only called when there is an error.
int WMaster::DataRead(void)
{
if (!open_ok) return 0;
if (!CheckSocket())
{
PrintErrNo();
return 0;
}
iResult = recv(ConnectSocket, (char *)input_buff,sizeof(input_buff),0);
if(iResult >= 0)
{
return iResult;
}
nError=WSAGetLastError();
if(nError==WSAEWOULDBLOCK) return iResult;
PrintErrNo();
return 0;
}
The fact that you are polling the socket every millisecond may have something to do with your performance problem. But I'd like to see the source to CheckSocket before concluding that as the problem.