sync: Always use WORKER_BATCH_SIZE

With 551285fa35, the comment about number
of workers no longer stands - dict is shared among multiprocesses and
real time information is available.

Using 2.7k projects as the baseline, using chunk size of 4 takes close
to 5 minutes. A chunk size of 32 takes this down to 40s - a reduction of
rougly 8 times which matches the increase.

R=gavinmak@google.com

Bug: b/371638995
Change-Id: Ida5fd8f7abc44b3b82c02aa0f7f7ae01dff5eb07
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/438523
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Tested-by: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

tests/test_subcmds_sync.py

@@ -355,6 +355,30 @@ class SafeCheckoutOrder(unittest.TestCase):
         )
 
 
+class Chunksize(unittest.TestCase):
+    """Tests for _chunksize."""
+
+    def test_single_project(self):
+        """Single project."""
+        self.assertEqual(sync._chunksize(1, 1), 1)
+
+    def test_low_project_count(self):
+        """Multiple projects, low number of projects to sync."""
+        self.assertEqual(sync._chunksize(10, 1), 10)
+        self.assertEqual(sync._chunksize(10, 2), 5)
+        self.assertEqual(sync._chunksize(10, 4), 2)
+        self.assertEqual(sync._chunksize(10, 8), 1)
+        self.assertEqual(sync._chunksize(10, 16), 1)
+
+    def test_high_project_count(self):
+        """Multiple projects, high number of projects to sync."""
+        self.assertEqual(sync._chunksize(2800, 1), 32)
+        self.assertEqual(sync._chunksize(2800, 16), 32)
+        self.assertEqual(sync._chunksize(2800, 32), 32)
+        self.assertEqual(sync._chunksize(2800, 64), 32)
+        self.assertEqual(sync._chunksize(2800, 128), 21)
+
+
 class GetPreciousObjectsState(unittest.TestCase):
     """Tests for _GetPreciousObjectsState."""