use replicateM mechanism of endpoint repetition rather than time based

lib/jormungandr/test/bench/Latency.hs

@@ -1,4 +1,3 @@
-{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE LambdaCase #-}
@@ -402,6 +401,10 @@ measureApiLogs = measureLatency
 sampleTimeSeconds :: Int
 sampleTimeSeconds = 1
 
+-- | Run tests for at least this long to get accurate timings.
+sampleNTimes :: Int
+sampleNTimes = 10
+
 -- | Measure how long an action takes based on trace points and taking an
 -- average of results over a short time period (also DB footprint).
 measureLatency
@@ -414,7 +417,7 @@ measureLatency
     -> IO ([NominalDiffTime], [NominalDiffTime])
 measureLatency start finish startDB stopDB tvar action = do
     atomically $ writeTVar tvar []
-    _res <- repeatFor sampleTimeSeconds action
+    replicateM_ sampleNTimes action
     extractTimings start finish startDB stopDB . reverse <$> readTVarIO tvar
 
 -- | Scan through iohk-monitoring logs and extract time differences between
@@ -451,22 +454,6 @@ extractTimings isStart isFinish isObserveStart isObserveStop msgs =
 
     getTimestamp = tstamp . loMeta
 
--- | Repeatedly run an action, until total elapsed time in seconds is greater
--- than the given amount.
-repeatFor :: Int -> IO a -> IO [a]
-repeatFor nSeconds action = do
-    start <- getSystemTime
-    let repeater rs = do
-            now <- getSystemTime
-            if finished start now
-                then pure rs
-                else do
-                    !r <- action
-                    repeater (r:rs)
-    reverse <$> repeater []
-  where
-    finished a b = systemSeconds b - systemSeconds a > fromIntegral nSeconds
-
 setupLatencyLogging
     :: TVar [LogObject ServerLog]
     -> IO (CM.Configuration, Trace IO ServerLog)