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diff --git a/testsuite/tests/concurrent/should_run/conc051.hs b/testsuite/tests/concurrent/should_run/conc051.hs
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+module Main (main) where
+
+import System.Environment
+import Control.Concurrent
+import Control.Monad
+
+-----------------------------------------------------------------------------
+-- test MVar throughput between the main thread and a child thread
+
+-- This test runs quite slowly on the threaded/SMP RTS vs. the normal RTS,
+-- because the main thread and child thread are run by different OS threads,
+-- so each MVar communication requires real OS thread switching.
+--
+-- Figures I get are about a factor of 10 difference in speed, at GHC 6.5.
+
+main = chanTest 300000
+
+chanTest :: Int -> IO ()
+chanTest n = do
+  chan <- newEmptyMVar
+  forkIO (writer chan n)
+  reader chan n
+
+reader chan 0 = return ()
+reader chan n = do
+  takeMVar chan
+  reader chan (n-1)
+
+writer chan 0 = return ()
+writer chan n = do
+  putMVar chan ()
+  writer chan (n-1)