diff --git a/packages/core/src/render3/PERF_NOTES.md b/packages/core/src/render3/PERF_NOTES.md
index d031899025..9a75641e00 100644
--- a/packages/core/src/render3/PERF_NOTES.md
+++ b/packages/core/src/render3/PERF_NOTES.md
@@ -64,3 +64,10 @@ for (var i = 0, keys = Object.keys(obj); i < keys.length; i++) {
   const key = keys[i];
 }
 ```
+
+## Recursive functions
+Avoid recursive functions when possible because they cannot be inlined.
+
+## Loops
+Don't use foreach, it can cause megamorphic function calls (depending on the browser) and function allocations.
+It is [a lot slower than regular `for` loops](https://jsperf.com/for-vs-foreach-misko)