use number of physical cores, not including hyper-threading

CPUCost is per physical core

1 files changed, 16 insertions, 3 deletions

diff --git a/ExpensiveHash.hs b/ExpensiveHash.hs
index fed6d18..5799d83 100644
--- a/ExpensiveHash.hs
+++ b/ExpensiveHash.hs
@@ -19,7 +19,9 @@ import Data.Time.Clock
 import Control.DeepSeq
 import Control.Monad
 import Data.Monoid
-import GHC.Conc (getNumProcessors)
+import Data.List
+import Data.Maybe
+import Text.Read
 
 -- | A hash that is expensive to calculate.
 --
@@ -48,6 +50,7 @@ expensiveHash (UseArgon2 cost opts) (Salt s) b = ExpensiveHash cost $
 
 benchmarkExpensiveHash :: Int -> ExpensiveHashTunable -> Cost op -> IO (BenchmarkResult (Cost op))
 benchmarkExpensiveHash rounds tunables@(UseArgon2 _ hashopts) expected = do
+	numcores <- fromIntegral <$> getNumCores
 	start <- getCurrentTime
 	forM_ [1..rounds] $ \_ -> do
 		let ExpensiveHash _ t = expensiveHash tunables
@@ -60,15 +63,25 @@ benchmarkExpensiveHash rounds tunables@(UseArgon2 _ hashopts) expected = do
 	-- The expected cost is for a single core, so adjust it
 	-- based on the number of cores, up to a maximum of the number
 	-- of threads that the hash is configred to use.
-	numcpus <- fromIntegral <$> getNumProcessors
 	let maxthreads = Argon2.hashParallelism hashopts
-	let usedcpus = if numcpus > maxthreads then maxthreads else numcpus
+	let usedcpus = if numcores > maxthreads then maxthreads else numcores
 	let adjustedexpected = mapCost (`div` fromIntegral usedcpus) expected
 	return $ BenchmarkResult
 		{ expectedBenchmark = adjustedexpected
 		, actualBenchmark = actual
 		}
 
+-- Number of physical cores. This is not the same as
+-- getNumProcessors, which includes hyper-threading.
+getNumCores :: IO Integer
+getNumCores = getmax . mapMaybe parse . lines <$> readFile "/proc/cpuinfo"
+  where
+	getmax [] = error "Unknown number of physical cores."
+	getmax l = maximum l
+	parse l
+		| "core id" `isPrefixOf` l = readMaybe $ dropWhile (/= ':') l
+		| otherwise = Nothing
+
 benchmarkTunables :: Tunables -> IO ()
 benchmarkTunables tunables = do
 	putStrLn "/proc/cpuinfo:"