Re: [RFC 00/17] Pile o' entry stack changes

[Ingo Molnar]

* Andy Lutomirski <luto@xxxxxxxxxx> wrote:

> On Wed, Sep 6, 2017 at 3:16 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> > Andy Lutomirski <luto@xxxxxxxxxx> writes:
> >>
> >>  - Lots of people (Linus included) have asked to convert the entry
> >>    code to pop registers on exit instead of movqing them off the
> >>    stack.  This makes a bunch of progress in that direction.
> >
> > You should benchmark it on Atoms. Likely it's a regression there
> > because they don't have the special PUSH/POP acceleration.
> 
> I'm not entirely sure this is a worthwhile reason.  Atom will lose a
> few cycles due to POP throughput, but there's a lot less decode
> bandwidth needed and we save a cache line or two.

I think we can also safely assume that Atom will eventually either join the
21st century or die out - mild Atom micro-costs are not a good reason to
complicate the entry code...

Thanks,

	Ingo