On Thu, Aug 09, 2007 at 03:47:57AM -0400, Chris Snook wrote:
>
> If they're not doing anything, sure. Plenty of loops actually do some sort
> of real work while waiting for their halt condition, possibly even work
> which is necessary for their halt condition to occur, and you definitely
> don't want to be doing cpu_relax() in this case. On register-rich
> architectures you can do quite a lot of work without needing to reuse the
> register containing the result of the atomic_read(). Those are precisely
> the architectures where barrier() hurts the most.
I have a problem with this argument. The same loop could be
using a non-atomic as long as the updaters are serialised. Would
you suggest that we turn such non-atomics into volatiles too?
Any loop that's waiting for an external halt condition either
has to schedule away (which is a barrier) or you'd be busy
waiting in which case you should use cpu_relax.
Do you have an example where this isn't the case?
Cheers,
--
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