AcceptTcpClientAsync lagging on multiply connections

Question

I have a server and a client connecting via a tcp connection. If several simultaneous connection requests are sent to the server, several connections are quickly created first, and then the clients start connecting at intervals of about a second.

I found only a dependency that as many clients quickly connect as there are processor cores.

Server code:

    class Program {
        static void Main(string[] args) {
            var loggerFactory = new LoggerFactory().AddNLog();
            var logger = loggerFactory.CreateLogger<Program>();

            var tcpListener = new TcpListener(IPAddress.Any, 9100);
            tcpListener.Start();

            var sem = new SemaphoreSlim(18, 18);
            while (true) {
                sem.Wait();

                tcpListener
                    .AcceptTcpClientAsync()
                    .ContinueWith(async task => {
                        logger.LogInformation("Client accepted");

                        sem.Release();
                    });
            }
        }
    }

Client code:

class Program {
        static void Main(string[] args) {
            var loggerFactory = new LoggerFactory().AddNLog();
            var logger = loggerFactory.CreateLogger<Program>();

            var clientCount = 100;
            for (int i = 0; i < clientCount; i++) {
                Task.Run(() => {
                    var guid = Guid.NewGuid();

                    var client = new TcpClient();
                    client.Connect(IPAddress.Loopback, 9100);

                    logger.LogInformation($"{guid} Connected");

                    Thread.Sleep(1000000);
                });
            }

            while (true) { }
        }
    }

Server log (Windows10 x64/6 cores/netcore2.2):

2019/04/24 10:59:50.270|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:50.295|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:50.296|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:50.296|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:50.297|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:50.297|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:51.252|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:52.252|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:53.252|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:54.252|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 10:59:55.252|INFO|Test.Server.Tcp.Program|Client accepted 

Server log (Kubuntu x64/8 cores/netcore2.2)

2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:42.464|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:50.937|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:17:59.941|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:18:09.943|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:18:21.446|INFO|Test.Server.Tcp.Program|Client accepted 
2019/04/24 11:18:33.449|INFO|Test.Server.Tcp.Program|Client accepted

How can I speed up client connections?

Answer 1

Working client code with TaskCreationOptions.LongRunning:

    class Program {
        static void Main(string[] args) {
            var loggerFactory = new LoggerFactory().AddNLog();
            var logger = loggerFactory.CreateLogger<Program>();

            var clientCount = 100;
            for (int i = 0; i < clientCount; i++) {
                var client = new TcpClient();
                client
                    .ConnectAsync(IPAddress.Loopback, 9100)
                    .ContinueWith(async task => {
                        await task;

                        logger.LogInformation("Connected");

                        await Task.Delay(1000000); // a lot of work
                    }, TaskContinuationOptions.LongRunning);
            }

            while (true) { }
        }
    }