[MIPS] Improve branch prediction in ll/sc atomic operations.
Now that finally all supported versions of binutils have functioning
support for .subsection use .subsection to tweak the branch prediction
I did not modify the R10000 errata variants because it seems unclear if
this will invalidate the workaround which actually relies on the cheesy
prediction of branch likely to cause a misspredict if the sc was
successful.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/include/asm-mips/spinlock.h b/include/asm-mips/spinlock.h
index fc3217f..f1755d2 100644
--- a/include/asm-mips/spinlock.h
+++ b/include/asm-mips/spinlock.h
@@ -3,7 +3,7 @@
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
- * Copyright (C) 1999, 2000, 06 by Ralf Baechle
+ * Copyright (C) 1999, 2000, 06 Ralf Baechle (ralf@linux-mips.org)
* Copyright (C) 1999, 2000 Silicon Graphics, Inc.
*/
#ifndef _ASM_SPINLOCK_H
@@ -49,11 +49,18 @@
__asm__ __volatile__(
" .set noreorder # __raw_spin_lock \n"
"1: ll %1, %2 \n"
- " bnez %1, 1b \n"
+ " bnez %1, 2f \n"
" li %1, 1 \n"
" sc %1, %0 \n"
- " beqz %1, 1b \n"
+ " beqz %1, 2f \n"
" nop \n"
+ " .subsection 2 \n"
+ "2: ll %1, %2 \n"
+ " bnez %1, 2b \n"
+ " li %1, 1 \n"
+ " b 1b \n"
+ " nop \n"
+ " .previous \n"
" .set reorder \n"
: "=m" (lock->lock), "=&r" (tmp)
: "m" (lock->lock)
@@ -99,8 +106,12 @@
"1: ll %0, %3 \n"
" ori %2, %0, 1 \n"
" sc %2, %1 \n"
- " beqz %2, 1b \n"
+ " beqz %2, 2f \n"
" andi %2, %0, 1 \n"
+ " .subsection 2 \n"
+ "2: b 1b \n"
+ " nop \n"
+ " .previous \n"
" .set reorder"
: "=&r" (temp), "=m" (lock->lock), "=&r" (res)
: "m" (lock->lock)
@@ -154,11 +165,18 @@
__asm__ __volatile__(
" .set noreorder # __raw_read_lock \n"
"1: ll %1, %2 \n"
- " bltz %1, 1b \n"
+ " bltz %1, 2f \n"
" addu %1, 1 \n"
" sc %1, %0 \n"
" beqz %1, 1b \n"
" nop \n"
+ " .subsection 2 \n"
+ "2: ll %1, %2 \n"
+ " bltz %1, 2b \n"
+ " addu %1, 1 \n"
+ " b 1b \n"
+ " nop \n"
+ " .previous \n"
" .set reorder \n"
: "=m" (rw->lock), "=&r" (tmp)
: "m" (rw->lock)
@@ -192,8 +210,12 @@
"1: ll %1, %2 \n"
" sub %1, 1 \n"
" sc %1, %0 \n"
- " beqz %1, 1b \n"
+ " beqz %1, 2f \n"
" nop \n"
+ " .subsection 2 \n"
+ "2: b 1b \n"
+ " nop \n"
+ " .previous \n"
" .set reorder \n"
: "=m" (rw->lock), "=&r" (tmp)
: "m" (rw->lock)
@@ -222,11 +244,18 @@
__asm__ __volatile__(
" .set noreorder # __raw_write_lock \n"
"1: ll %1, %2 \n"
- " bnez %1, 1b \n"
+ " bnez %1, 2f \n"
" lui %1, 0x8000 \n"
" sc %1, %0 \n"
- " beqz %1, 1b \n"
+ " beqz %1, 2f \n"
" nop \n"
+ " .subsection 2 \n"
+ "2: ll %1, %2 \n"
+ " bnez %1, 2b \n"
+ " lui %1, 0x8000 \n"
+ " b 1b \n"
+ " nop \n"
+ " .previous \n"
" .set reorder \n"
: "=m" (rw->lock), "=&r" (tmp)
: "m" (rw->lock)
@@ -322,12 +351,15 @@
" bnez %1, 2f \n"
" lui %1, 0x8000 \n"
" sc %1, %0 \n"
- " beqz %1, 1b \n"
- " nop \n"
- __WEAK_ORDERING_MB
- " li %2, 1 \n"
- " .set reorder \n"
+ " beqz %1, 3f \n"
+ " li %2, 1 \n"
"2: \n"
+ __WEAK_ORDERING_MB
+ " .subsection 2 \n"
+ "3: b 1b \n"
+ " li %2, 0 \n"
+ " .previous \n"
+ " .set reorder \n"
: "=m" (rw->lock), "=&r" (tmp), "=&r" (ret)
: "m" (rw->lock)
: "memory");