On Oct 31, 2018, at 3:11 AM, Peter Zijlstra [off-list ref] wrote:

quoted

On Wed, Oct 31, 2018 at 12:15:46AM +0200, Igor Stoppa wrote:
On 30/10/2018 23:02, Andy Lutomirski wrote:

quoted

quoted

But I dislike allowing regular writes in the protected region. We
really only need four write primitives:

1. Just write one value.  Call at any time (except NMI).

2. Just copy some bytes. Same as (1) but any number of bytes.

3,4: Same as 1 and 2 but must be called inside a special rare write
region. This is purely an optimization.

Atomic? RCU?

RCU can be done, that's not really a problem. Atomics otoh are a
problem. Having pointers makes them just work.

Andy; I understand your reason for not wanting them, but I really don't
want to duplicate everything. Is there something we can do with static
analysis to make you more comfortable with the pointer thing?

I’m sure we could do something with static analysis, but I think seeing a real use case where all this fanciness makes sense would be good.

And I don’t know if s390 *can* have an efficient implementation that uses pointers. OTOH they have all kinds of magic stuff, so who knows?