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Re: [RFC 3/5] powerpc: atomic: implement atomic{,64}_{add,sub}_return_* variants

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Hi Peter,

On Fri, Aug 28, 2015 at 12:48:54PM +0200, Peter Zijlstra wrote:
> On Fri, Aug 28, 2015 at 10:48:17AM +0800, Boqun Feng wrote:
> > +/*
> > + * Since {add,sub}_return_relaxed and xchg_relaxed are implemented with
> > + * a "bne-" instruction at the end, so an isync is enough as a acquire barrier
> > + * on the platform without lwsync.
> > + */
> > +#ifdef CONFIG_SMP
> > +#define smp_acquire_barrier__after_atomic() \
> > +	__asm__ __volatile__(PPC_ACQUIRE_BARRIER : : : "memory")
> > +#else
> > +#define smp_acquire_barrier__after_atomic() barrier()
> > +#endif
> > +#define arch_atomic_op_acquire(op, args...)				\
> > +({									\
> > +	typeof(op##_relaxed(args)) __ret  = op##_relaxed(args);		\
> > +	smp_acquire_barrier__after_atomic();				\
> > +	__ret;								\
> > +})
> > +
> > +#define arch_atomic_op_release(op, args...)				\
> > +({									\
> > +	smp_lwsync();							\
> > +	op##_relaxed(args);						\
> > +})
> 
> Urgh, so this is RCpc. We were trying to get rid of that if possible.
> Lets wait until that's settled before introducing more of it.
> 
> lkml.kernel.org/r/20150820155604.GB24100@arm.com

OK, get it. Thanks.

So I'm not going to introduce these arch specific macros, I think what I
need to implement are just _relaxed variants and cmpxchg_acquire.

Regards,
Boqun

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[RFC 0/5] atomics: powerpc: implement relaxed/acquire/release variants of some atomics Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 04:50 +0200
  [RFC 4/5] powerpc: atomic: implement xchg_* and atomic{,64}_xchg_* variants Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 04:50 +0200
  [RFC 3/5] powerpc: atomic: implement atomic{,64}_{add,sub}_return_* variants Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 04:50 +0200
    Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Peter Zijlstra <peterz@infradead.org> - 2015-08-28 12:50 +0200
      Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 14:10 +0200
        Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 16:20 +0200
          Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Peter Zijlstra <peterz@infradead.org> - 2015-08-28 17:40 +0200
            Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 19:00 +0200
            Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Will Deacon <will.deacon@arm.com> - 2015-09-01 21:10 +0200
              Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-01 23:50 +0200
                Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Will Deacon <will.deacon@arm.com> - 2015-09-02 12:00 +0200
                Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-02 13:00 +0200
                Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Pranith Kumar <bobby.prani@gmail.com> - 2015-09-02 17:30 +0200
                Re: [RFC 3/5] powerpc: atomic: implement atomic{,64}_{add,sub}_return_*  variants Pranith Kumar <bobby.prani@gmail.com> - 2015-09-02 17:40 +0200
                Re: [RFC 3/5] powerpc: atomic: implement  atomic{,64}_{add,sub}_return_* variants Will Deacon <will.deacon@arm.com> - 2015-09-03 12:40 +0200
  [RFC 5/5] powerpc: atomic: implement cmpxchg{,64}_* and atomic{,64}_cmpxchg_* variants Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 04:50 +0200
  [RFC 1/5] atomics: add test for atomic operations with _relaxed variants Boqun Feng <boqun.feng@gmail.com> - 2015-08-28 04:50 +0200

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