update based on profiling

While L.toStrict copies, profiling showed it was only around 0.3% of
git-annex find runtime. Does not seem worth optimising that, which would
probably involve either a major refactoring, or a use of
UnsafeInterleaveIO.

Also, it seems to me that the latter would need to read chunks, and
preappend the leftover part to the next chunk. But a strict ByteString
append itself is a copy, so I'm not convinced that would be faster than
L.toStrict.

Git/Command.hs

@@ -101,10 +101,8 @@ pipeNullSplit params repo = do
 	(s, cleanup) <- pipeReadLazy params repo
 	return (filter (not . L.null) $ L.split 0 s, cleanup)
 
-{- Reads lazily, but converts each part to a strict ByteString for
+{- Reads lazily, but copies each part to a strict ByteString for
  - convenience.
- -
- - FIXME the L.toStrict makes a copy, more expensive than ideal.
  -}
 pipeNullSplit' :: [CommandParam] -> Repo -> IO ([S.ByteString], IO Bool)
 pipeNullSplit' params repo = do

doc/todo/optimize_by_converting_String_to_ByteString.mdwn

@@ -14,8 +14,9 @@ the `bs` branch has quite a lot of things still needing work, including:
   decodeBS conversions. Or at least most of them. There are likely
   quite a few places where a value is converted back and forth several times.
 
-  It would be good to instrument them with Debug.Trace and find out which
-  are the hot ones that get called, and focus on those.
+  As a first step, profile and look for the hot spots. For example, keyFile
+  uses fromRawFilePath and that adds around 3% overhead in `git-annex find`. 
+  Converting it to a RawFilePath needs a version of `</>` for RawFilePaths.
 
 * System.FilePath is not available for RawFilePath, and many of the
   conversions are to get a FilePath in order to use that library.
@@ -29,6 +30,4 @@ the `bs` branch has quite a lot of things still needing work, including:
   windows, so a compatability shim will be needed.
   (I can't seem to find any library that provides one.)
 
-* Eliminate some Data.ByteString.Lazy.toStrict, which is a slow copy.
-
 * Use ByteString for parsing git config to speed up startup.