On Fri, 22 Feb 2019, Christopher Lameter wrote:

> On Fri, 22 Feb 2019, Björn Töpel wrote:
> 
> > > The problem is that the register needs to be referenced by the amo
> > > instruction. Can amoadd increment an address relative to a scratch
> > > register?
> > >
> >
> > It cannot. So, we'll end up with (at least) a preempt disabled region...
> 
> If we need to do that then we already have so much overhead due to that
> processing that it may not be worthwhile. lc/sc overhead is minor compared
> to switching preempt on and off I think.

Is it strictly necessary to disable and re-enable preemption?  

On a UMA system, it might be preferable to risk the cost of the cache line 
bounce than to flip preemption off and on - assuming there's no other 
impact.


- Paul