Fix T16916 CI failures (#16966)

1. Slightly increased the waiting time for the tested effect to be more
   profound.

2. Introduced measuring of the actual time spent waiting and adjusing
   CPU time by it to compensate for threadDelay waiting time
   inconsistencies.

1 files changed, 8 insertions, 4 deletions

diff --git a/testsuite/tests/lib/base/T16916.hs b/testsuite/tests/lib/base/T16916.hs
index a5dafa515b..6084c95572 100644
--- a/testsuite/tests/lib/base/T16916.hs
+++ b/testsuite/tests/lib/base/T16916.hs
@@ -2,6 +2,7 @@ module Main where
 
 import Control.Concurrent
 import Foreign.C
+import GHC.Clock
 import GHC.Event
 import System.CPUTime
 import System.Posix.Types
@@ -21,12 +22,15 @@ makeTestSocketFd = do
 callback :: FdKey -> Event -> IO ()
 callback _ _ = return ()
 
-idleCpuUsage :: IO Integer
+-- Idle CPU usage with 0 for 0% and 10^12 for 100%
+idleCpuUsage :: IO Double
 idleCpuUsage = do
+  startTime <- getMonotonicTime
   startCPUTime <- getCPUTime
-  threadDelay 500000
+  threadDelay 1000000
   endCPUTime <- getCPUTime
-  return $ endCPUTime - startCPUTime
+  endTime <- getMonotonicTime
+  return $ fromIntegral (endCPUTime - startCPUTime) / (endTime - startTime)
 
 main :: IO ()
 main = do
@@ -42,4 +46,4 @@ main = do
 
   -- CPU consumption should roughly be the same when just idling vs
   -- when idling after the event been triggered
-  print $ (fromIntegral eventTriggeredUsage / fromIntegral noEventUsage) < 2.0
+  print $ eventTriggeredUsage / noEventUsage < 2.0