[PATCH] powerpc: Spinlock optimization and cleanup

[Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>]

This patch optimizes powerpc spinlock implementation by:

* Current algorithm spin over a lwzx, but only after issuing a lwarx.
  first.  The optimization for such case is to avoid the first lwarx
  in contention case (which is much more costly than normal loads).

* Use the correct EH hint bit on the larx for supported ISA.  For lock
  acquisition, the thread that acquired the lock with a successful stcx
  do not want to give away the write ownership on the cacheline. The
  idea is to make the load reservation "sticky" about retaining write
  authority to the line.  That way, the store that must inevitably come
  to release the lock can succeed quickly and not contend with other
  threads issuing lwarx.  If another thread does a store to the line
  (false sharing), the winning thread must give up write authority to
  The proper value of EH for the larx for a lock acquisition is 1.

It also adds some cleanup to use the defined acquire semantic
instructions and function prototype using default C style.

Tested on powerpc32-fpu and powerpc64.

--

	* sysdeps/powerpc/nptl/pthread_spin_lock.c (pthread_spin_lock):
	Optimize first check for contention case and add lwarx hint.
	* sysdeps/powerpc/nptl/pthread_spin_trylock.c (pthread_spin_trylock):
	Use ANSI prototype.
	* sysdep/unix/sysv/linux/powerpc/pthread_spin_unlock.c: Move to ...
	* sysdeps/powerpc/nptl/pthread_spin_unlock.c: ... here.

---

diff --git a/sysdeps/powerpc/nptl/pthread_spin_lock.c b/sysdeps/powerpc/nptl/pthread_spin_lock.c
index cc081f8..8a39da9 100644
--- a/sysdeps/powerpc/nptl/pthread_spin_lock.c
+++ b/sysdeps/powerpc/nptl/pthread_spin_lock.c
@@ -19,24 +19,26 @@
 #include "pthreadP.h"
 
 int
-pthread_spin_lock (lock)
-     pthread_spinlock_t *lock;
+pthread_spin_lock (pthread_spinlock_t *lock)
 {
   unsigned int __tmp;
 
   asm volatile (
-       "1:	lwarx	%0,0,%1\n"
+       "0:	lwzx    %0,0,%1\n"
+       "	cmpwi   0,%0,0\n"
+       "	bne	0b\n"
+       "1:	lwarx	%0,0,%1" MUTEX_HINT_ACQ "\n"
        "	cmpwi	0,%0,0\n"
        "	bne-	2f\n"
        "	stwcx.	%2,0,%1\n"
        "	bne-	2f\n"
-       "	isync\n"
-       "	.subsection 1\n"
-       "2:	lwzx	%0,0,%1\n"
-       "	cmpwi	0,%0,0\n"
-       "	bne	2b\n"
-       "	b	1b\n"
-       "	.previous"
+                __ARCH_ACQ_INSTR "\n"
+       "        .subsection 1\n"
+       "2:	lwzx    %0,0,%1\n"
+       "        cmpwi   0,%0,0\n"
+       "        bne     2b\n"
+       "        b       1b\n"
+       "        .previous"
        : "=&r" (__tmp)
        : "r" (lock), "r" (1)
        : "cr0", "memory");
diff --git a/sysdeps/powerpc/nptl/pthread_spin_trylock.c b/sysdeps/powerpc/nptl/pthread_spin_trylock.c
index 77a4615..c485aa4 100644
--- a/sysdeps/powerpc/nptl/pthread_spin_trylock.c
+++ b/sysdeps/powerpc/nptl/pthread_spin_trylock.c
@@ -20,8 +20,7 @@
 #include "pthreadP.h"
 
 int
-pthread_spin_trylock (lock)
-     pthread_spinlock_t *lock;
+pthread_spin_trylock (pthread_spinlock_t *lock)
 {
   unsigned int old;
   int err = EBUSY;
diff --git a/sysdeps/powerpc/nptl/pthread_spin_unlock.c b/sysdeps/powerpc/nptl/pthread_spin_unlock.c
new file mode 100644
index 0000000..7af694f
--- /dev/null
+++ b/sysdeps/powerpc/nptl/pthread_spin_unlock.c
@@ -0,0 +1,28 @@
+/* pthread_spin_unlock -- unlock a spin lock.  PowerPC version.
+   Copyright (C) 2007-2015 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/>.  */
+
+#include "pthreadP.h"
+#include <lowlevellock.h>
+
+int
+pthread_spin_unlock (pthread_spinlock_t *lock)
+{
+  __asm __volatile (__ARCH_REL_INSTR ::: "memory");
+  *lock = 0;
+  return 0;
+}
diff --git a/sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c b/sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c
deleted file mode 100644
index 7af694f..0000000
--- a/sysdeps/unix/sysv/linux/powerpc/pthread_spin_unlock.c
+++ /dev/null
@@ -1,28 +0,0 @@
-/* pthread_spin_unlock -- unlock a spin lock.  PowerPC version.
-   Copyright (C) 2007-2015 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/>.  */
-
-#include "pthreadP.h"
-#include <lowlevellock.h>
-
-int
-pthread_spin_unlock (pthread_spinlock_t *lock)
-{
-  __asm __volatile (__ARCH_REL_INSTR ::: "memory");
-  *lock = 0;
-  return 0;
-}