ASV: DataFrame.__setitem__ performance with object dtype (#55938)

* add asv

* add github issue context

* fix minor

Author: quangngd

asv_bench/benchmarks/indexing.py

@@ -515,6 +515,18 @@ def time_setitem_list(self):
         self.df[[100, 200, 300]] = 100
 
 
+class SetitemObjectDtype:
+    # GH#19299
+
+    def setup(self):
+        N = 1000
+        cols = 500
+        self.df = DataFrame(index=range(N), columns=range(cols), dtype=object)
+
+    def time_setitem_object_dtype(self):
+        self.df.loc[0, 1] = 1.0
+
+
 class ChainIndexing:
     params = [None, "warn"]
     param_names = ["mode"]