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 Signed-off-by: Paul Burton <[email protected]> --- arch/mips/Kconfig | 1 + arch/mips/include/asm/spinlock.h | 5 +++++ 2 files changed, 6 insertions(+) diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index f501665..ec6b430 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -3,6 +3,7 @@ config MIPS 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 diff --git a/arch/mips/include/asm/spinlock.h b/arch/mips/include/asm/spinlock.h index 1fca2e0..418a5acb 100644 --- a/arch/mips/include/asm/spinlock.h +++ b/arch/mips/include/asm/spinlock.h @@ -42,6 +42,11 @@ static inline int arch_spin_is_locked(arch_spinlock_t *lock) return ((counters >> 16) ^ counters) & 0xffff; } +static inline int arch_spin_value_unlocked(arch_spinlock_t lock) +{ + return lock.h.serving_now == lock.h.ticket; +} + #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock) #define arch_spin_unlock_wait(x) \ while (arch_spin_is_locked(x)) { cpu_relax(); } -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
