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MIPS: Select CONFIG_ARCH_USE_CMPXCHG_LOCKREF for MIPS64

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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>
This commit is contained in:
Paul Burton 2015-07-30 08:16:10 -07:00 committed by Ralf Baechle
parent f51246efee
commit 5fac4f7ac0
2 changed files with 6 additions and 0 deletions
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1
arch/mips/Kconfig
View File

@ -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

5
arch/mips/include/asm/spinlock.h
View File

@ -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(); }