On Thu, Aug 16, 2007 at 04:56:21PM +1000, Paul Mackerras wrote:
quoted text
>
> Note that I said these are the cases _where one might want to allow
> caching_, so of course adding volatile doesn't help _these_ cases.
> There are of course other cases where one definitely doesn't want to
> allow the compiler to cache the value, such as when polling an atomic
> variable waiting for another CPU to change it, and from my inspection
> so far these cases seem to be the majority.

We've been through that already.  If it's a busy-wait it
should use cpu_relax.  If it's scheduling away that already
forces the compiler to reread anyway.

Do you have an actual example where volatile is needed?

quoted text
> - It matches the normal expectation based on the name "atomic_read"
> - It matches the behaviour of the other atomic_* primitives

Can't argue since you left out what those expectations
or properties are.

quoted text
> - It avoids bugs in the cases where "volatile" behaviour is required

Do you (or anyone else for that matter) have an example of this?

Cheers,
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