Fix

docs/lang/articles/performance_tuning/performance.md

@@ -238,6 +238,9 @@ We address this problem by introducing the *offline* cache feature, which dumps
   * `'lru'`: Discards the cached files least used recently;
   * `'fifo'`: Discards the cached files added in the earliest.
 
+To verify the effect, run some examples twice and observe the launch overhead:
+![](../static/assets/effect_of_offline_cache.png)
+
 :::note
 If your code behaves abnormally, disable offline cache by setting the environment variable `TI_OFFLINE_CACHE=0` or `offline_cache=False` in the `ti.init()` method call and file an issue with us on [Taichi's GitHub repo](https://github.com/taichi-dev/taichi/issues/new/choose).
 :::