Messages in this thread | | | Date | Wed, 20 Apr 2016 16:24:08 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V3] powerpc: Implement {cmp}xchg for u8 and u16 |
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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?
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