Re: Q: schedule() and implied barriers on arm64

[Peter Zijlstra]

On Mon, Oct 19, 2015 at 09:06:05AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > In any case, its all moot now, since Paul no longer requires schedule() to imply 
> > a full barrier.
> >
> > [...]
> 
> Nevertheless from a least-surprise POV it might be worth guaranteeing it, because 
> I bet there's tons of code that assumes that schedule() is a heavy operation and 
> it's such an easy mistake to make. Since we are so close to having that guarantee, 
> we might as well codify it?
> 
> Just like system calls are assumed to be barriers in general - 

Are they? I know they are on some platforms, but I'm not sure we've
audited them all and established this.

> and system calls are more lightweight than schedule() ...

Hopefully, although if you enable nohz_full there's a fair chance to
reverse that :-)
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