Commit 5fac4f7a authored Jul 30, 2015 by Paul Burton Committed by Ralf Baechle Sep 03, 2015

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>

parent f51246ef

arch/mips/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -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

arch/mips/include/asm/spinlock.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -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(); }

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