[PATCH] aarch64: Optimized implementation of pthread_spin_lock and unlock

[Xuelei Zhang <zhangxuelei4 at huawei dot com>]

An optimized algorithm of spin_lock is implemented to wait for
random time in the case that multi-threads want to store spinlock
at the same time. This way can make the operation of different
threads asynchronous, thereby reducing bus conflicts, and futherly
improving the overall performance, which benefits more on aarch64
for its multi-core features.

In addition, the assembly version of spin_unlock is also implemented.
---
 sysdeps/aarch64/nptl/pthread_spin_lock.S   | 103 +++++++++++++++++++++++++++++
 sysdeps/aarch64/nptl/pthread_spin_unlock.S |  34 ++++++++++
 2 files changed, 137 insertions(+)
 create mode 100644 sysdeps/aarch64/nptl/pthread_spin_lock.S
 create mode 100644 sysdeps/aarch64/nptl/pthread_spin_unlock.S

diff --git a/sysdeps/aarch64/nptl/pthread_spin_lock.S b/sysdeps/aarch64/nptl/pthread_spin_lock.S
new file mode 100644
index 00000000000..662410c5fa3
--- /dev/null
+++ b/sysdeps/aarch64/nptl/pthread_spin_lock.S
@@ -0,0 +1,103 @@
+/* pthread_spin_lock -- lock a spin lock. Generic version.
+   Copyright (C) 2012-2019 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ */
+
+ENTRY (pthread_spin_lock)
+	DELOUSE (0)
+
+	mov	w1, #0x1
+
+L(spin):
+	prfm	pldl1strm, [x0]
+    /* A count to distinguish wating time.
+    The larger the value, the more intense the current lock
+    conflicts, and the longer the waiting time. */
+	add	w3, w3, #0x1
+	ldaxr	w2, [x0]
+	cbnz	w2, L(spin)
+	stxr	w2, w1, [x0]
+	cbnz	w2, 1f
+	b	L(end)
+
+L(end):
+	mov w0, #0x0
+	ret
+
+    /* Set the loop times of L(wait) from 1000 to 7000 cycles,
+    equals waiting 1~2us per 1000 cycles. */
+	.p2align 4
+7:
+	mov	w6, #0x1b58
+	b	L(wait_init)
+6:
+	mov	w6, #0x1770
+	b	L(wait_init)
+5:
+	mov	w6, #0x1388
+	b	L(wait_init)
+4:
+	mov	w6, #0x0fa0
+	b	L(wait_init)
+3:
+	mov	w6, #0x0bb8
+	b	L(wait_init)
+2:
+	mov	w6, #0x07d0
+	b	L(wait_init)
+1:
+	mov	w6, #0x03e8
+	b	L(wait_init)
+
+L(wait_init):
+	mov	w5, #0x0
+L(wait):
+	add	w5, w5, #0x1
+	cmp	w5, w6
+	b.lt	L(wait) /* Wait ends when w5 equals w6. */
+
+L(stxr_try):
+	ldr	w2, [x0]
+	cbz	w2, L(spin)
+	and	w3, w3, #0x07
+    /* 8 kinds of distinguish wating time 
+    based on the lower three bits of w3. */
+	cmp	w3, #0x01
+	beq	1b
+	cmp	w3, #0x02
+	beq	2b
+	cmp	w3, #0x03
+	beq	3b
+	cmp	w3, #0x04
+	beq	4b
+	cmp	w3, #0x05
+	beq	5b
+	cmp	w3, #0x06
+	beq	6b
+	cmp	w3, #0x07
+	beq	7b
+
+	wfe /* w3=0x000: the most intense situation so to wait 50 us */
+	b	L(stxr_try)
+
+
+END (pthread_spin_lock)
+libc_hidden_builtin_def (pthread_spin_lock)
+weak_alias (pthread_spin_lock, index)
diff --git a/sysdeps/aarch64/nptl/pthread_spin_unlock.S b/sysdeps/aarch64/nptl/pthread_spin_unlock.S
new file mode 100644
index 00000000000..57a6bca86fe
--- /dev/null
+++ b/sysdeps/aarch64/nptl/pthread_spin_unlock.S
@@ -0,0 +1,34 @@
+/* pthread_spin_unlock -- unlock a spin lock. Generic version.
+   Copyright (C) 2012-2019 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ */
+
+ENTRY (pthread_spin_unlock)
+	DELOUSE (0)
+	stlr	wzr, [x0]
+	mov	w0, #0x0
+	ret
+
+END (pthread_spin_unlock)
+libc_hidden_builtin_def (pthread_spin_unlock)
+weak_alias (pthread_spin_unlock, index)
-- 
2.14.1.windows.1