mempool-bench: add a message warning that the benchmark can fail intermittently due to unrelated load on the CI runner

Author: fraser-iohk

ouroboros-consensus/bench/mempool-bench/Main.hs

@@ -23,6 +23,7 @@ import           Main.Utf8 (withStdTerminalHandles)
 import           Ouroboros.Consensus.Ledger.SupportsMempool (ByteSize32)
 import qualified Ouroboros.Consensus.Mempool.Capacity as Mempool
 import           System.Exit (die, exitFailure)
+import           System.IO (hPutStrLn, stderr)
 import qualified Test.Consensus.Mempool.Mocked as Mocked
 import           Test.Consensus.Mempool.Mocked (MockedMempool)
 import           Test.Tasty (withResource)
@@ -46,7 +47,9 @@ main = withStdTerminalHandles $ do
           Nothing               -> exitFailure
           Just    runIngredient -> do
             success <- runIngredient
-            unless success exitFailure
+            unless success $ do
+              hPutStrLn stderr "This benchmark is flaky in GitHub Actions due to CI runner load, which can it to run significantly slower than expected. It may be useful to try to re-run the job if it fails."
+              exitFailure
       where
         benchmarkJustAddingTransactions =
             bgroup "Just adding" $