MIPS: Select CONFIG_ARCH_USE_CMPXCHG_LOCKREF for MIPS64
On MIPS64 we have spinlocks that are 32b in size and an efficient
cmpxchg64 implementation, so we qualify to make use of cmpxchg backed
lockrefs. Select the ARCH_USE_CMPXCHG_LOCKREF Kconfig symbol and provide
a trivial implementation of arch_spin_value_unlocked to satisfy the
lockref code.
Using Linus' simple testcase from
http://article.gmane.org/gmane.linux.file-systems/77466 on a dual core
system with an in-development MIPS64 CPU running on FPGA I see around an
8% gain:
Pre-patch:
Total loops: 252698
Total loops: 251482
Total loops: 250806
Total loops: 252885
Total loops: 251666
Post-patch:
Total loops: 273728
Total loops: 269932
Total loops: 269341
Total loops: 275004
Total loops: 270208
[ralf@linux-mips.org: Fixed conflict.]
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Cc: Maciej W. Rozycki <macro@codesourcery.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/10810/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 3c2e4c8..449f840 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -3,6 +3,7 @@
default y
select ARCH_MIGHT_HAVE_PC_PARPORT
select ARCH_MIGHT_HAVE_PC_SERIO
+ select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
select HAVE_CONTEXT_TRACKING
select HAVE_GENERIC_DMA_COHERENT
select HAVE_IDE