Re: [Ltt-dev] [PATCH] local_t : Documentation - update

* Mathieu Desnoyers ([email protected]) wrote:
> > So it is "one cpu may write, other cpus may read", and as big as
> > long. Are you sure obscure architectures (sparc?) can implement this
> > in useful way? ... maybe yes, unless obscure architecture exists where
> > second other cpu can see garbage data when first cpu writes into long
> > ...?
> > 
> > 
> 
> Sparc64 uses a memory barrier around the atomic operations in the SMP case
> (see arch/sparc64/lib/atomic.S). The same is true for sparc. As I am not a sparc
> expert, I left the asm-generic default behavior, but I think it should be safe
> to implement local.S code derived from atomic.S to optimize the speed of the
> local_t operations on sparc and sparc64. Can anyone confirm this ?
> 

Sorry for the self reply.. looking at arch/sparc/lib/atomic32.c tells me that
local.h could use its own version that would only disable interrupts without
taking any hashed spinlock.

sparc64 seems to be a saner architecture providing atomic operations wrt the
local CPU. A barrier-free version of arch/sparc64/lib/atomic.S would improve
performance.

Mathieu

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