diff --git a/doc/optimization.txt b/doc/optimization.txt
index fdcaa6ea5c..832cdffb6b 100644
--- a/doc/optimization.txt
+++ b/doc/optimization.txt
@@ -174,6 +174,9 @@ SPARC-specific:
 SPARC Joint Programming Specification (JPS1): Commonality
 http://www.fujitsu.com/downloads/PRMPWR/JPS1-R1.0.4-Common-pub.pdf
 
+UltraSPARC III Processor User's Manual (contains instruction timings)
+http://www.sun.com/processors/manuals/USIIIv2.pdf
+
 
 GCC asm links:
 official doc but quite ugly