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[RFC PATCH]: Align large allocations to cacheline


This patch aligns allocations of large blocks to a cacheline on ARM and AArch64. The main goal is to
reduce performance variations due to random alignment choices, however it improves performance on
several benchmarks as well. SPECFP2000 improves by ~1.5%.

Any comments?

ChangeLog:
2014-10-29  Wilco Dijkstra  <wdijkstr@arm.com>

	* malloc/malloc.c (__libc_malloc): Add support for aligning large blocks.
	* sysdeps/unix/sysv/linux/aarch64/malloc-sysdep.h: New file.
	New defines (MALLOC_LARGE_BLOCK_ALIGN), (MALLOC_LARGE_BLOCK_SIZE).
	* sysdeps/unix/sysv/linux/arm/malloc-sysdep.h: Likewise.

---
 malloc/malloc.c                                 |    8 ++++++++
 sysdeps/unix/sysv/linux/aarch64/malloc-sysdep.h |   23 +++++++++++++++++++++++
 sysdeps/unix/sysv/linux/arm/malloc-sysdep.h     |   23 +++++++++++++++++++++++
 3 files changed, 54 insertions(+)
 create mode 100644 sysdeps/unix/sysv/linux/aarch64/malloc-sysdep.h
 create mode 100644 sysdeps/unix/sysv/linux/arm/malloc-sysdep.h

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 6cbe9f3..0b0466e 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2878,6 +2878,14 @@ __libc_malloc (size_t bytes)
   mstate ar_ptr;
   void *victim;
 
+#ifdef MALLOC_LARGE_BLOCK_ALIGN
+  if (bytes > MALLOC_LARGE_BLOCK_SIZE)
+    {
+      void *address = RETURN_ADDRESS (0);
+      return _mid_memalign (MALLOC_LARGE_BLOCK_ALIGN, bytes, address);
+    }
+#endif
+
   void *(*hook) (size_t, const void *)
     = atomic_forced_read (__malloc_hook);
   if (__builtin_expect (hook != NULL, 0))
diff --git a/sysdeps/unix/sysv/linux/aarch64/malloc-sysdep.h
b/sysdeps/unix/sysv/linux/aarch64/malloc-sysdep.h
new file mode 100644
index 0000000..3fe9f72
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/aarch64/malloc-sysdep.h
@@ -0,0 +1,23 @@
+/* System-specific malloc support functions.  AArch64 version.
+   Copyright (C) 2012-2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#define MALLOC_LARGE_BLOCK_ALIGN (64)
+#define MALLOC_LARGE_BLOCK_SIZE (16384)
+
+#include_next <malloc-sysdep.h>
+
diff --git a/sysdeps/unix/sysv/linux/arm/malloc-sysdep.h
b/sysdeps/unix/sysv/linux/arm/malloc-sysdep.h
new file mode 100644
index 0000000..3fe9f72
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/malloc-sysdep.h
@@ -0,0 +1,23 @@
+/* System-specific malloc support functions.  AArch64 version.
+   Copyright (C) 2012-2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#define MALLOC_LARGE_BLOCK_ALIGN (64)
+#define MALLOC_LARGE_BLOCK_SIZE (16384)
+
+#include_next <malloc-sysdep.h>
+
-- 
1.7.9.5



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