From 72ca834ae8a86cef59035a05042988298715269c Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 7 Jun 2020 21:24:21 +0300
Subject: [PATCH] Change yield_k to not use sp_thread_yield; using
 sp_thread_sleep is always strictly superior, at least on Windows

---
 include/boost/smart_ptr/detail/yield_k.hpp | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/boost/smart_ptr/detail/yield_k.hpp b/include/boost/smart_ptr/detail/yield_k.hpp
index 367e022..8f52a58 100644
--- a/include/boost/smart_ptr/detail/yield_k.hpp
+++ b/include/boost/smart_ptr/detail/yield_k.hpp
@@ -175,14 +175,17 @@ namespace detail
 
 inline void yield( unsigned k ) BOOST_NOEXCEPT
 {
-    if( k < 16 )
+    // Experiments show that a simple sp_thread_sleep() here is best;
+    // leave a few pause instructions out of mostly superstition.
+    // (These are verified to not degrade performance.)
+    //
+    // There seems to be no benefit from calling sp_thread_yield()
+    // at any time.
+
+    if( k < 8 )
     {
         BOOST_SMT_PAUSE
     }
-    else if( k < 32 )
-    {
-        sp_thread_yield();
-    }
     else
     {
         sp_thread_sleep();