Re: Synchronizing Bit operations V2

[Christoph Lameter]

On Fri, 31 Mar 2006, Andi Kleen wrote:

> On Friday 31 March 2006 18:22, Hans Boehm wrote:
> 
> > My impression is that approach (1) tends not to stick, since it involves
> > a substantial performance hit on architectures on which the fence is
> > not implicitly included in atomic operations.  Those include Itanium and
> > PowerPC.
> 
> At least the PPC people are eating the overhead because back when they
> didn't they had a long string of subtle powerpc only bugs caused by that

PPC has barriers for both smb_mb_before/after cases. IMHO we should do the 
same for ia64 and not fuzz around.

> It's a stability/maintainability vs performance issue. I doubt the 
> performance advantage would be worth the additional work. I guess
> with the engineering time you would need to spend getting all this right
> you could do much more fruitful optimizations.

Agreed.

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