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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>