Update perf map docs (#68181)

* update doc

Co-authored-by: Noah Falk <noahfalk@users.noreply.github.com>

diff --git a/docs/project/linux-performance-tracing.md b/docs/project/linux-performance-tracing.md
index 720c54c..bc198d3 100644 (file)
--- a/docs/project/linux-performance-tracing.md
+++ b/docs/project/linux-performance-tracing.md
@@ -48,11 +48,14 @@ Follow these steps to prepare your machine to collect a performance trace.
 1. Have two shell windows available - one for controlling tracing, referred to as **[Trace]**, and one for running the application, referred to as **[App]**.
 2. **[App]** Setup the application shell - this enables tracing configuration inside of CoreCLR.
 
-       > ```bash
+    > ```bash
        > export COMPlus_PerfMapEnabled=1
        > export COMPlus_EnableEventLog=1
        > ```
 
+   Note:
+   COMPlus_PerfMapEnabled will cause the .NET runtime to write a file containing symbolic information for managed code to the disk. Depending on the performance of your disk and the amount of managed code in the application this could have a significant performance overhead.
+
 3. **[Trace]** Start collection.
 
        > ```bash