[Haskell-cafe] Slow mvar when compiled with threaded

[Bob Ippolito]

On Tuesday, January 7, 2014, Branimir Maksimovic wrote:

>  On 01/08/2014 04:15 AM, Bob Ippolito wrote:
>
> On Tuesday, January 7, 2014, Branimir Maksimovic wrote:
>
>> On 01/07/2014 09:39 PM, Bob Ippolito wrote:
>>
>>> Here's a much simpler implementation for that sort of pattern, using
>>> channels to fan out work to threads. I added a dependency on Criterion
>>> because getCPUTime is basically useless for this kind of measurement on Mac
>>> OS X since it doesn't include the time that the process spent waiting on IO:
>>>
>> Great, thank you very much. You gave me material for learning ;)
>> However, my version is significantly faster when compiling without
>> -threaded.
>> With -threaded option, your version is much faster than mine, but both
>> are significantly slower
>> then compile without -threaded.
>>
>
>  Happy to look into it, I didn't have time today to do benchmarks
> (and Mac OS X is the worst platform to do this kind of testing on
> regardless of language, its network stack is inconsistent at best). I need
> to know more:
>
>  How exactly are you compiling?
>
>
> ghc-7.6.3 --make -O2 client.hs
>
>  Which OS?
>
>
> Ubuntu 13.10 with 3.13-rc7 kernel.
>
>  What version of GHC and Haskell Platform?
>
>
> bmaxa at maxa:~$ apt-cache policy haskell-platform
> haskell-platform:
>   Installed: 2013.2.0.0
>   Candidate: 2013.2.0.0
>   Version table:
>  *** 2013.2.0.0 0
>         500 http://archive.ubuntu.com/ubuntu/ saucy/universe amd64
> Packages
>         100 /var/lib/dpkg/status
>
>
>  What is the exact command line you execute it with?
>
>
> time ./client maxa 5055 1000 100000
>

What happens if you add +RTS -N to the end of that command line?


>
>
>  What timings do you get?
>
> with your version:
> real    0m4.235s
> user    0m1.589s
> sys    0m2.642s
>
> with my version
> real    0m3.010s
> user    0m0.590s
> sys    0m2.417s
> that is, of course, without -threaded
>
>  What's the code for the server are you connecting to?
>
> import Network (listenOn,PortID(..))
> import Network.Socket (accept,close)
> import Network.Socket.ByteString
> import System.Environment
> import Control.Concurrent (forkIO)
>
> main = do
>     n <- getArgs
>     let nn = (read.head) n :: Int
>     putStrLn $ "Listening on " ++ show nn
>     sock <- listenOn $ PortNumber $ fromIntegral nn
>     serve sock
>
> serve sock = do
>     (s,_) <- accept sock
>     forkIO $ process s
>     serve sock
>
> process sock = do
>     buf <- recv sock 1024
>     sendAll sock buf
>     close sock
>
>  Loopback, local network, or internet?
>
>
> loopback. Testing is on same computer.
>
> Thanks!
>

Great, I'll look closer later tonight or tomorrow morning.
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