Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

From: Herbert Xu
Date: Thu Aug 16 2007 - 03:10:50 EST


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,
--
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/