recv() is Missing from Results

[Alon_Tal]

[cpp]The following snippet produces results which I think might be faulty. After profiling, I am not seeing any calls to recv(), neither using sampling nor using call-graph runs.

I run this tester and stream UDP traffic to it, and wait until it exits (After 20000 packets).
The results attribute the highest "self time" to cout related operations (put(), operator<<), which is unlikely, as they only get called 24 times, whereas recv() gets called thousands of times, and should be quite expensive.

My question: How can I see how much time was spent in recv()?



#include 
#include 
#include 

using std::cerr;
using std::cout;
using std::endl;

int main()
{
    int sock = -1;
    int retval = 0;

    sock = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock == -1)
    {
        cerr << "Failed to allocate socket. Error " << sock << " (" << strerror(errno) << ")" << endl;
        return 1;
    }

    sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(51258);
    addr.sin_addr.s_addr = INADDR_ANY;
    socklen_t socklen = sizeof(addr);

    retval = bind(sock, (const sockaddr*)&addr, socklen);
    if (retval == -1)
    {
        cerr << "Failed to bind socket. Error " << sock << " (" << strerror(errno) << ")" << endl;
        return 1;
    }

    cout << "Calling recv()..." << endl;

    char buf[1024] = {0};

    int i = 0;
    while (1)
    {
        retval = recv(sock, buf, sizeof(buf), 0);
        if (retval == -1)
        {
            cerr << "Failed to recv. Error " << sock << " (" << strerror(errno) << ")" << endl;
            return 1;
        }

        if (i++ % 1000 == 0)
        {
            cout << "Received " << retval << " bytes" << endl;

            if (i > 20000)
            {
                cout << "Stopping" << endl;
                break;
            }
        }
    }
[/cpp]

[David_A_Intel1]

Sampling will not catch it unless significant time is spent in the recv() routine and call graph won't record it if it is ring0 code. Is recv() a kernel call. Also, are you sure it is not inlined by the compiler? Are you building with optimizations on or off?