On Thu, 2007-07-12 at 05:14 +0200, Nick Piggin wrote:
> Here is a set of patches that aims to mitigate some of the lock_page
> overhead on powerpc introduced in the fault path by another set.
> Fortunately it also improves various other things too :)
Some nits...
> +static __inline__ void clear_bit_unlock(int nr, volatile unsigned long *addr)
> +{
> + unsigned long old;
> + unsigned long mask = BITOP_MASK(nr);
> + unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
> +
> + __asm__ __volatile__(
> + LWSYNC_ON_SMP
> +"1:" PPC_LLARX "%0,0,%3 # clear_bit_unlock\n"
> + "andc %0,%0,%2\n"
> + PPC405_ERR77(0,%3)
> + PPC_STLCX "%0,0,%3\n"
> + "bne- 1b"
> + : "=&r" (old), "+m" (*p)
> + : "r" (mask), "r" (p)
> + : "cc" );
> +}
You also want a "memory" clobber on clear_bit_unlock() to tell gcc to
consider it as a barrier for memory accesses.
In addition, it's worth documenting that while spin_unlock() provides
synchronization with outstanding MMIOs (look at the io sync stuff we
have in spinlock.h), these bitops don't (and I don't want to add that
here anyway), so drivers abusing bitops for lock might want to use
mmiowb() explicitely.
> +static __inline__ void __clear_bit_unlock(int nr, volatile unsigned long
> *addr)
> +{
> + __asm__ __volatile__(LWSYNC_ON_SMP);
> + __clear_bit(nr, addr);
> +}
The above needs a "memory" clobber too.
Cheers,
Ben.
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