On Wed, Apr 20, 2016 at 09:24:00PM +0800, Pan Xinhui wrote:
> +#define __XCHG_GEN(cmp, type, sfx, skip, v) \
> +static __always_inline unsigned long \
> +__cmpxchg_u32##sfx(v unsigned int *p, unsigned long old, \
> + unsigned long new); \
> +static __always_inline u32 \
> +__##cmp##xchg_##type##sfx(v void *ptr, u32 old, u32 new) \
> +{ \
> + int size = sizeof (type); \
> + int off = (unsigned long)ptr % sizeof(u32); \
> + volatile u32 *p = ptr - off; \
> + int bitoff = BITOFF_CAL(size, off); \
> + u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff; \
> + u32 oldv, newv, tmp; \
> + u32 ret; \
> + oldv = READ_ONCE(*p); \
> + do { \
> + ret = (oldv & bitmask) >> bitoff; \
> + if (skip && ret != old) \
> + break; \
> + newv = (oldv & ~bitmask) | (new << bitoff); \
> + tmp = oldv; \
> + oldv = __cmpxchg_u32##sfx((v u32*)p, oldv, newv); \
> + } while (tmp != oldv); \
> + return ret; \
> +}
So for an LL/SC based arch using cmpxchg() like that is sub-optimal.
Why did you choose to write it entirely in C?
