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[patches] Avoid uses of swp on ARM
- To: patches@xxxxxxxxxx
- Subject: [patches] Avoid uses of swp on ARM
- From: "Joseph S. Myers" <joseph@xxxxxxxxxxxxxxxx>
- Date: Mon, 6 Aug 2007 13:11:11 +0000 (UTC)
I've applied this patch to avoid uses of swp in pthread_spin_lock and
pthread_spin_trylock on ARM, since this is very slow on ARMv6; the kernel
helpers should be used instead.
Index: ChangeLog.eglibc
===================================================================
--- ChangeLog.eglibc (revision 3060)
+++ ChangeLog.eglibc (working copy)
@@ -1,3 +1,13 @@
+2007-08-06 Zack Weinberg <zack@xxxxxxxxxxxxxxxx>
+
+ * sysdeps/arm/nptl/pthread_spin_lock.S
+ * sysdeps/arm/nptl/pthread_spin_trylock.S: Delete.
+ * sysdeps/arm/nptl/pthread_spin_lock.c
+ * sysdeps/arm/nptl/pthread_spin_trylock.c: New files using <atomic.h>
+ primitives to take spinlocks.
+ * sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h: Use kernel helpers
+ unconditionally.
+
2007-08-06 Paul Brook <paul@xxxxxxxxxxxxxxxx>
* sysdeps/arm/dl-machine.h (elf_machine_dynamic): Add missing
Index: sysdeps/arm/nptl/pthread_spin_trylock.S
===================================================================
--- sysdeps/arm/nptl/pthread_spin_trylock.S (revision 3060)
+++ sysdeps/arm/nptl/pthread_spin_trylock.S (working copy)
@@ -1,34 +0,0 @@
-/* Copyright (C) 2005 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. */
-
-#define _ERRNO_H 1
-#include <bits/errno.h>
-
-#include <sysdep.h>
-
- .text
- .align 4
-
-ENTRY (pthread_spin_trylock)
- mov r1, #1
- swp r2, r1, [r0]
- teq r2, #0
- moveq r0, #0
- movne r0, #EBUSY
- PSEUDO_RET_NOERRNO
-END (pthread_spin_trylock)
Index: sysdeps/arm/nptl/pthread_spin_trylock.c
===================================================================
--- sysdeps/arm/nptl/pthread_spin_trylock.c (revision 0)
+++ sysdeps/arm/nptl/pthread_spin_trylock.c (revision 0)
@@ -0,0 +1,27 @@
+/* Copyright (C) 2005, 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 <errno.h>
+#include <atomic.h>
+#include "pthreadP.h"
+
+int
+pthread_spin_trylock (pthread_spinlock_t *lock)
+{
+ return atomic_compare_and_exchange_val_acq(lock, 1, 0) ? EBUSY : 0;
+}
Index: sysdeps/arm/nptl/pthread_spin_lock.S
===================================================================
--- sysdeps/arm/nptl/pthread_spin_lock.S (revision 3060)
+++ sysdeps/arm/nptl/pthread_spin_lock.S (working copy)
@@ -1,31 +0,0 @@
-/* Copyright (C) 2005 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 <sysdep.h>
-
- .text
- .align 4
-
-ENTRY (pthread_spin_lock)
- mov r1, #1
-1: swp r2, r1, [r0]
- teq r2, #0
- bne 1b
- mov r0, #0
- PSEUDO_RET_NOERRNO
-END (pthread_spin_lock)
Index: sysdeps/arm/nptl/pthread_spin_lock.c
===================================================================
--- sysdeps/arm/nptl/pthread_spin_lock.c (revision 0)
+++ sysdeps/arm/nptl/pthread_spin_lock.c (revision 0)
@@ -0,0 +1,30 @@
+/* Copyright (C) 2005, 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 <atomic.h>
+#include "pthreadP.h"
+
+int
+pthread_spin_lock (pthread_spinlock_t *lock)
+{
+ while (atomic_compare_and_exchange_val_acq(lock, 1, 0) != 0)
+ while (*lock != 0)
+ ;
+
+ return 0;
+}
Index: sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h
===================================================================
--- sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h (revision 3060)
+++ sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h (working copy)
@@ -37,29 +37,6 @@
void __arm_link_error (void);
-#ifdef UP
-
-/* We require kernel assisted barriers for SMP safety, so it is only worth
- defining this on UP. */
-#define atomic_exchange_acq(mem, newvalue) \
- ({ __typeof (*mem) result; \
- if (sizeof (*mem) == 1) \
- __asm__ __volatile__ ("swpb %0, %1, [%2]" \
- : "=&r,&r" (result) \
- : "r,0" (newvalue), "r,r" (mem) : "memory"); \
- else if (sizeof (*mem) == 4) \
- __asm__ __volatile__ ("swp %0, %1, [%2]" \
- : "=&r,&r" (result) \
- : "r,0" (newvalue), "r,r" (mem) : "memory"); \
- else \
- { \
- result = 0; \
- abort (); \
- } \
- result; })
-
-#else
-
#ifdef __thumb2__
#define atomic_full_barrier() \
__asm__ __volatile__ \
@@ -76,8 +53,6 @@
: : : "ip", "lr", "cc", "memory");
#endif
-#endif
-
/* Atomic compare and exchange. This sequence relies on the kernel to
provide a compare and exchange operation which is atomic on the
current architecture, either via cleverness on pre-ARMv6 or via
--
Joseph S. Myers
joseph@xxxxxxxxxxxxxxxx