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POHaskell - Slow socket connection when threaded
 

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    <p>I've started with Haskell a while ago and now I'm focusing on networking. I followed some tutorials and source samples to put together a very simple echo server:</p> <pre><code>main = withSocketsDo $ do forkIO $ acceptor 8080 print "Server running ... " &gt;&gt; getLine &gt;&gt;= print tcpSock :: IO Socket tcpSock = socket AF_INET Stream 0 acceptor :: PortNumber -&gt; IO () acceptor port = do -- Setup server socket sock &lt;- tcpSock setSocketOption sock ReuseAddr 1 bindSocket sock (SockAddrInet port iNADDR_ANY) listen sock 50 -- Start with zero index loop sock 0 where loop sock sockId = do -- Accept socket (nextSock, addr) &lt;- accept sock -- Setup the socket for performance (_, handle) &lt;- setupClient nextSock -- Run client in own thread forkIO $ do -- Get a stream of bytes stream &lt;- BS.hGetContents handle -- Echo the first received char BS.hPut handle $ BS.take 1 stream -- Kill the socket SIO.hClose handle -- Accept next client loop sock (sockId + 1) setupClient :: Socket -&gt; IO (Socket, SIO.Handle) setupClient sock = do -- Disable nagle setSocketOption sock NoDelay 1 -- Disable buffering hdl &lt;- socketToHandle sock SIO.ReadWriteMode SIO.hSetBuffering hdl SIO.NoBuffering return (sock, hdl) </code></pre> <p>Now, I've tested the code with the ab-Tool to benchmark the server. The code is compiled using -O2 and -threaded and the program is started using +RTS -N to use multiple OS threads.</p> <p>The code creates a new lightweight thread per client and as far as I remember are these threads pretty cheap because they are scheduled by a bunch of real OS threads.</p> <p>After running the tool, the results are:</p> <p>ab -n 10000 -c 1000 <code>http://localhost:8080/</code> ~ 500 - 1600 req/sec Yes, it does change sometimes between 500 and 1600!</p> <p>At first I thought well, not bad. Then I ran the program without "+RTS -N" and results are almost every time ~20000 req/sec.</p> <p>Obviously the threading kills the performance pretty badly, but why ? My guess is, that the IO manager does a pretty bad job when dealing with a lot of connections.</p> <p>BTW: I use Ubuntu 13.04 and ghc 7.6, but I've tested the code under Windows 8 which gave me far worse results, but I think the IO manager is tuned for linux, which makes sense.</p> <p>Am I doing something reallly stupid here ?? I know, the example is quite trivial but here is obviously something going wrong.</p> <p>Regards, Chris</p>
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    1. COis that 20 or 20000 in 20.000
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    2. COIt's 20000, sry for the misunderstanding
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    3. COHow many actual threads does your processor have and how many real threads are you using (the argument to -N)
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