Messages in this thread | | | Date | Fri, 16 Feb 2018 11:35:20 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 3/5] asm-generic/bitops/atomic.h: Rewrite using atomic_fetch_* |
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On Thu, Feb 15, 2018 at 06:20:49PM +0000, Will Deacon wrote:
> > The only other comment is that I think it would be better if you use > > atomic_t instead of atomic_long_t. It would just mean changing > > BIT_WORD() and BIT_MASK(). > > It would make it pretty messy for big-endian architectures, I think...
Urgh, the big.little indians strike again.. Bah I always forget about that.
#define BIT_U32_MASK(nr) (1UL << ((nr) % 32)) #define BIT_U32_WORD(nr) (((nr) / 32) ^ (4 * __BIG_ENDIAN__))
Or something like that might work, but I always get these things wrong.
> > The reason is that we generate a pretty sane set of atomic_t primitives > > as long as the architecture supplies cmpxchg, but atomic64 defaults to > > utter crap, even on 64bit platforms. > > I think all the architectures using this today are 32-bit: > > blackfin > c6x > cris > metag > openrisc > sh > xtensa > > and I don't know how much we should care about optimising the generic atomic > bitops for 64-bit architectures that rely on spinlocks for 64-bit atomics!
You're probably right, but it just bugs me that we default to such horrible crap. Arguably we should do a better default for atomic64_t on 64bit archs. But that's for another time.
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