Hi all, This is a question specific to the Yesod framework, but simple enough (I hope) to be considered a beginner question... I am puzzled by the performance of these two very simple web-servers, one written in Warp and another written in Yesod: === YESOD === {-# LANGUAGE TypeFamilies, QuasiQuotes, MultiParamTypeClasses, TemplateHaskell #-} import Yesod data HelloWorld = HelloWorld mkYesod "HelloWorld" [parseRoutes| / HomeR GET |] instance Yesod HelloWorld getHomeR :: Handler RepHtml getHomeR = defaultLayout [whamlet|$newline always Hello World! |] main :: IO () -- main = warpDebug 3000 HelloWorld main = warp 3000 HelloWorld === WARP === {-# LANGUAGE OverloadedStrings #-} import Network.Wai import Network.HTTP.Types import Network.Wai.Handler.Warp (run) import Data.ByteString.Lazy.Char8 () app :: Application app _ = return $ responseLBS status200 [("Content-Type", "text/html")] "Hello, Warp!" main :: IO () main = do putStrLn "http://localhost:8080/" run 8080 app === I've tested both using httperf: $> httperf --hog --client=0/1 --server=localhost --port=3000 --uri=/ --rate=1000 --send-buffer=4096 --recv-buffer=16384 --num-conns=100 --num-calls=100 --burst-length=20 and I got very different results: YESOD: Request rate: 4048.0 req/s (0.2 ms/req) WARP: Request rate: 33656.2 req/s (0.0 ms/req) Now, I understand that Yesod is expected to be slower than the "raw" Warp, but I wasn't expecting a 10x slowdown, especially for such a trivial Yesod app (no db, no auth, etc.). [ Compilation command was: ghc -Wall -O2 --make yesod.hs $ yesod version yesod-core version:1.1.0 ] What is going on? Thanks, L.