Re: [PATCH] Re: Profiling broken on x86?

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Jul 08, 2022 at 12:17:25PM +0000, Emmanuel Dreyfus wrote:
> On Fri, Jul 08, 2022 at 11:55:13AM +0200, Manuel Bouyer wrote:
> > I think it's more than this; it's to use the right instruction on the
> > right CPU. But I don't remember the details
> 
> This tests a CPU features at boot time, and replaces a generic implementation
> by a CPU-optimized one. 
> 
> Indeed it brings maximum performance because there is no CPU feature test
> at runtime, but it comes with a price. Profilig and debugging are broken,
> for instance.

that's not the only story. See the Opteron workaround for example.
It enables SMAP if available, too. 

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--