It's nonsense to compare switches of native thread and green thread (https://ruby-china.org/topics/20367)

thread_switch.hs

import Control.Concurrent
import Control.Monad
import Data.IORef

main = do
    c   <- newIORef (0::Int)
    arr <- newIORef []

    replicateM_ 100 $ forkIO $ thread c

    replicateM_ 20 $ do
        v <- readIORef c
        putStrLn $ "c = " ++ show v
        when (v /= 0) $ modifyIORef' arr (v:)
        writeIORef c 0
        threadDelay (10 ^ 6)

    a <- readIORef arr
    print $ fromIntegral (sum a) `div` length a


thread c = forever $ do
    modifyIORef' c  (+1)
    yield