> Anyway, I'm attaching my completely mindless test program. It has
> hacky things like "unsigned long count[MAXTHREADS][32]" which are
> purely to just spread out the counts so that they aren't in the same
> cacheline etc.
>
> Also note that the performance numbers it spits out depend a lot on
> tings like how long the dcache hash chains etc are, so they are not
> really reliable. Running the test-program right after reboot when the
> dentries haven't been populated can result in much higher numbers -
> without that having anything to do with contention or locking at all.
Running on a POWER7 here with 32 threads (8 cores x 4 threads) I'm
getting some good improvements:
Without patch:
# ./t
Total loops: 3730618
With patch:
# ./t
Total loops: 16826271
The numbers move around about 10% from run to run. I didn't change your
program at all, so it's still running with MAXTHREADS 16.
powerpc patch below. I'm using arch_spin_is_locked() to implement
arch_spin_value_unlocked().
Mikey
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 9cf59816d..4a3f86b 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -139,6 +139,7 @@ config PPC
select OLD_SIGSUSPEND
select OLD_SIGACTION if PPC32
select HAVE_DEBUG_STACKOVERFLOW
+ select ARCH_USE_CMPXCHG_LOCKREF
config EARLY_PRINTK
bool
diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index 5b23f91..65c25272 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -156,6 +156,11 @@ extern void arch_spin_unlock_wait(arch_spinlock_t *lock);
do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
#endif
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+ return !arch_spin_is_locked(&lock);
+}
+
/*
* Read-write spinlocks, allowing multiple readers
* but only one writer.
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