From 5b0a86c5c045a2c24ae4fde3ba98e191f1b1dbfe Mon Sep 17 00:00:00 2001
From: Daniel Black <daniel@linux.ibm.com>
Date: Tue, 26 Nov 2019 11:43:47 +1100
Subject: [PATCH] define linker section for global variables POC

---
 include/my_compiler.h           |  2 ++
 sql/CMakeLists.txt              |  6 +++++-
 sql/mysqld.ld                   | 21 +++++++++++++++++++++
 storage/innobase/btr/btr0sea.cc |  4 ++--
 4 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 sql/mysqld.ld

diff --git a/include/my_compiler.h b/include/my_compiler.h
index 2c3daee5ad0..32462534836 100644
--- a/include/my_compiler.h
+++ b/include/my_compiler.h
@@ -187,4 +187,6 @@ struct my_aligned_storage
 # define SUPPRESS_UBSAN
 #endif
 
+#define MY_GLOBAL __attribute((section (".data.read_mostly")))
+
 #endif /* MY_COMPILER_INCLUDED */
diff --git a/sql/CMakeLists.txt b/sql/CMakeLists.txt
index 88e17c0d941..49b04311c2a 100644
--- a/sql/CMakeLists.txt
+++ b/sql/CMakeLists.txt
@@ -465,7 +465,6 @@ ADD_DEPENDENCIES(sqlgunitlib GenError)
 
 ######################### GUnit Lib #################################
 
-
 IF(WIN32)
   SET(MYSQLD_SOURCE main.cc nt_servc.cc nt_servc.h message.rc)
 ELSE()
@@ -556,6 +555,11 @@ IF(WITH_MYSQLD_LDFLAGS)
      "${MYSQLD_LINK_FLAGS} ${WITH_MYSQLD_LDFLAGS}")
 ENDIF()
 
+IF(NOT MSVC)
+  SET_TARGET_PROPERTIES(mysqld PROPERTIES LINK_DEPENDS ${CMAKE_SOURCE_DIR}/sql/mysqld.ld)
+  TARGET_LINK_OPTIONS(mysqld BEFORE PRIVATE LINKER:-T,${CMAKE_SOURCE_DIR}/sql/mysqld.ld)
+ENDIF()
+
 # Help INSTALL_DEBUG_TARGET to locate it
 SET_TARGET_PROPERTIES(mysqld PROPERTIES
     RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
diff --git a/sql/mysqld.ld b/sql/mysqld.ld
new file mode 100644
index 00000000000..b7bdc64ea24
--- /dev/null
+++ b/sql/mysqld.ld
@@ -0,0 +1,21 @@
+/*
+
+Linker script to create a .data.read_mostly section with ELF linkers.
+
+This, with the approprate variable attributes, keeps read only variables being
+linked adjacent to hot variable (like pseudo number or statistic counters).
+
+256 (bytes) is from the largest cache-line size (s390) on current hardware.
+This ensures that the section afterwards is on a different cache line.  As
+we are inserting after .rodata, an initial alignment isn't needed.
+
+*/
+
+SECTIONS
+{
+    .data.read_mostly : {
+      *(.data.read_mostly)
+      . = ALIGN(256);
+    }
+}
+INSERT AFTER .rodata
diff --git a/storage/innobase/btr/btr0sea.cc b/storage/innobase/btr/btr0sea.cc
index 085ec33ce8b..0d53b937c02 100644
--- a/storage/innobase/btr/btr0sea.cc
+++ b/storage/innobase/btr/btr0sea.cc
@@ -55,10 +55,10 @@ Created 2/17/1996 Heikki Tuuri
 
 /** Is search system enabled.
 Search system is protected by array of latches. */
-char		btr_search_enabled	= true;
+char		btr_search_enabled	MY_GLOBAL = true;
 
 /** Number of adaptive hash index partition. */
-ulong		btr_ahi_parts		= 8;
+ulong		btr_ahi_parts		MY_GLOBAL = 8;
 
 #ifdef UNIV_SEARCH_PERF_STAT
 /** Number of successful adaptive hash index lookups */
-- 
2.21.0