1 files changed, 3 insertions, 0 deletions

diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt
index d330fe3103da..ea5a827395dd 100644
--- a/Documentation/ftrace.txt
+++ b/Documentation/ftrace.txt
@@ -291,6 +291,9 @@ explains which is which.
   CPU#: The CPU which the process was running on.
 
   irqs-off: 'd' interrupts are disabled. '.' otherwise.
+            Note: If the architecture does not support a way to
+                  read the irq flags variable, an 'X' will always
+                  be printed here.
 
   need-resched: 'N' task need_resched is set, '.' otherwise.