From 92091c4b81248bcc9bea2b868bdd7d5703ad0038 Mon Sep 17 00:00:00 2001
From: Titus Winters <titus@google.com>
Date: Wed, 17 Feb 2016 10:57:02 -0500
Subject: [PATCH] A more numeric reason for targeted optimization.

---
 CppCoreGuidelines.md | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md
index 4731486..f56c19f 100644
--- a/CppCoreGuidelines.md
+++ b/CppCoreGuidelines.md
@@ -9945,7 +9945,13 @@ Optimizing a non-performance-critical part of a program has no effect on system
 ##### Note
 
 If your program spends most of its time waiting for the web or for a human, optimization of in-memory computation is probably useless.
-???
+
+Put another way: If your program spends 4% of its processing time doing
+computation A and 40% of its time doing computation B, a 50% improvement on A is
+only as impactful as a 5% improvement on B. (If you don't even know how much
+time is spent on A or B, see <a href="#Rper-reason">PER.1</a> and <a
+href="#Rper-Knuth">PER.2</a>.)
+
 
 ### <a name="Rper-simple"></a>PER.4: Don't assume that complicated code is necessarily faster than simple code