Re: I/O write ordering

James Bottomley
2004-09-22T14:48:53Z

On Wed, 2004-09-22 at 10:32, Matthew Wilcox wrote:
> I think the only disagreement is whether we have it implicit or explicit.
> I see three potential solutions:
>
> 1. iomb() [we have mb(), rmb(), wmb() already. Does mb() imply iomb()?
> Vice versa?]
> 2. io_spin_unlock() which is an io barrier as well as a memory barrier.
> 3. Make spin_unlock an io barrier. Expensive.
>
> I'd quite like to hear opinions from the PPC and Alpha people, they seem to
> be the most out-of-order architectures.

I favour 1. iomb; I think, since I/O barriers can be either heavyweight
or non-existent depending on the architecture, iomb() should imply mb()
but not vice versa.

James