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[PATCH] Optimise PowerPC Linux pthread_spin_unlock


We can use lwsync instead of sync when unlocking a spinlock. Testing a
pthread_spin_lock/pthread_spin_unlock pair on a POWER5 box we see a
speedup as expected:

baseline:	148.51 cycles
patched:	130.17 cycles

Anton
--

2007-08-09  Anton Blanchard  <anton@samba.org>

	* sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c: New file.

diff -ruN libc/nptl/sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c libc.work/nptl/sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c
--- libc/nptl/sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c	1969-12-31 18:00:00.000000000 -0600
+++ libc.work/nptl/sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c	2007-08-09 13:53:09.000000000 -0500
@@ -0,0 +1,29 @@
+/* pthread_spin_unlock -- unlock a spin lock.  PowerPC version.
+   Copyright (C) 2007 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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include "pthreadP.h"
+#include <lowlevellock.h>
+
+int
+pthread_spin_unlock (pthread_spinlock_t *lock)
+{
+  __asm __volatile (__lll_rel_instr ::: "memory");
+  *lock = 0;
+  return 0;
+}


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