From b2017b91a5572f7bc2caf15082b4b105f3a3e21d Mon Sep 17 00:00:00 2001
From: Rickard Green <rickard@erlang.org>
Date: Sun, 23 Feb 2014 20:04:30 +0100
Subject: Introduce configure option --with-assumed-cache-line-size=SIZE

---
 HOWTO/INSTALL.md                                 |  5 +++++
 erts/configure.in                                | 19 +++++++++++++++++++
 erts/emulator/beam/erl_alloc.h                   |  4 ++--
 erts/include/internal/ethread.h                  |  2 +-
 erts/include/internal/ethread_header_config.h.in |  2 ++
 5 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/HOWTO/INSTALL.md b/HOWTO/INSTALL.md
index c9f4062b83..fb18676699 100644
--- a/HOWTO/INSTALL.md
+++ b/HOWTO/INSTALL.md
@@ -274,6 +274,11 @@ Some of the available `configure` options are:
     `(g)cc`
 *   `--enable-m32-build` - Build 32-bit binaries using the `-m32` flag to
     `(g)cc`
+*   `--with-assumed-cache-line-size=SIZE` - Set assumed cache-line size in
+    bytes. Default is 64. Valid values are powers of two between and
+    including 16 and 8192. The runtime system use this value in order to
+    try to avoid false sharing. A too large value wastes memory. A to
+    small value will increase the amount of false sharing.
 *   `--{with,without}-termcap` - termcap (without implies that only the old
     Erlang shell can be used)
 *   `--with-javac=JAVAC` - Specify Java compiler to use
diff --git a/erts/configure.in b/erts/configure.in
index 02e5d12918..d71a264066 100644
--- a/erts/configure.in
+++ b/erts/configure.in
@@ -347,6 +347,25 @@ AS_HELP_STRING([--enable-clock-gettime],
     *) clock_gettime_correction=yes ;;
   esac ], clock_gettime_correction=unknown)
 
+AC_ARG_WITH(assumed-cache-line-size,
+AS_HELP_STRING([--with-assumed-cache-line-size=SIZE],
+               [specify assumed cache line size in bytes (valid values are powers of two between and including 16 and 8192; default is 64)]))
+
+dnl Require the assumed cache-line size to be a power of two between 16 and 8192
+case "$with_assumed_cache_line_size" in
+     ""|no|yes)
+	with_assumed_cache_line_size=64;;
+     16|32|64|128|256|512|1024|2048|4096|8192)
+	;;
+     *)
+	AC_MSG_ERROR([Invalid assumed cache-line size of $with_assumed_cache_line_size bytes])
+	;;
+esac
+
+AC_DEFINE_UNQUOTED(ASSUMED_CACHE_LINE_SIZE,
+		   $with_assumed_cache_line_size,
+		   [Assumed cache-line size (in bytes)])
+
 dnl Magic test for clearcase.
 OTP_RELEASE=
 if test "${ERLANG_COMMERCIAL_BUILD}" != ""; then
diff --git a/erts/emulator/beam/erl_alloc.h b/erts/emulator/beam/erl_alloc.h
index f83f6b39cf..942eaa47d0 100644
--- a/erts/emulator/beam/erl_alloc.h
+++ b/erts/emulator/beam/erl_alloc.h
@@ -209,8 +209,8 @@ int erts_is_allctr_wrapper_prelocked(void);
 void *erts_alloc_permanent_cache_aligned(ErtsAlcType_t type, Uint size);
 
 #ifndef ERTS_CACHE_LINE_SIZE
-/* Assume a cache line size of 64 bytes */
-#  define ERTS_CACHE_LINE_SIZE ((UWord) 64)
+/* Assumed cache line size */
+#  define ERTS_CACHE_LINE_SIZE ((UWord) ASSUMED_CACHE_LINE_SIZE)
 #  define ERTS_CACHE_LINE_MASK (ERTS_CACHE_LINE_SIZE - 1)
 #endif
 
diff --git a/erts/include/internal/ethread.h b/erts/include/internal/ethread.h
index 38b8e9e9b6..3a676e2a36 100644
--- a/erts/include/internal/ethread.h
+++ b/erts/include/internal/ethread.h
@@ -60,7 +60,7 @@
 #endif
 
 /* Assume 64-byte cache line size */
-#define ETHR_CACHE_LINE_SIZE 64
+#define ETHR_CACHE_LINE_SIZE ASSUMED_CACHE_LINE_SIZE
 #define ETHR_CACHE_LINE_MASK (ETHR_CACHE_LINE_SIZE - 1)
 
 #define ETHR_CACHE_LINE_ALIGN_SIZE(SZ) \
diff --git a/erts/include/internal/ethread_header_config.h.in b/erts/include/internal/ethread_header_config.h.in
index dd3599f86d..b36322490a 100644
--- a/erts/include/internal/ethread_header_config.h.in
+++ b/erts/include/internal/ethread_header_config.h.in
@@ -235,3 +235,5 @@
 /* Define if you want to turn on extra sanity checking in the ethread library */
 #undef ETHR_XCHK
 
+/* Assumed cache-line size (in bytes) */
+#undef ASSUMED_CACHE_LINE_SIZE
-- 
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