Issue #8873: add a documentation note about possible performance issues with the
default of unbuffered IO in subprocess.Popen.
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 19a8b6b..b5e769c 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -94,6 +94,12 @@
size. A negative *bufsize* means to use the system default, which usually means
fully buffered. The default value for *bufsize* is :const:`0` (unbuffered).
+ .. note::
+
+ If you experience performance issues, it is recommended that you try to
+ enable buffering by setting *bufsize* to either -1 or a large enough
+ positive value (such as 4096).
+
The *executable* argument specifies the program to execute. It is very seldom
needed: Usually, the program to execute is defined by the *args* argument. If
``shell=True``, the *executable* argument specifies which shell to use. On Unix,