On Thu, Aug 16, 2007 at 04:56:21PM +1000, Paul Mackerras wrote:

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?

- 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.

- 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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