Re: [PATCH v3] x86/vdso: Handle clock_gettime(CLOCK_TAI) in vDSO

From: Thomas Gleixner
Date: Wed Sep 12 2018 - 10:18:34 EST

On Wed, 12 Sep 2018, Florian Weimer wrote:
> On 09/09/2018 10:05 PM, Thomas Gleixner wrote:
> > See the patch below. It's integrating TAI without slowing down everything
> > and it definitely does not result in indirect calls.
> >
> > On a HSW it slows down clock_gettime() by ~0.5ns. On a SKL I get a speedup
> > by ~0.5ns. On a AMD Epyc server it's 1.2ns speedup. So it somehow depends
> > on the uarch and I also observed compiler version dependend variations.
> Does this mean glibc can keep using a single vDSO entrypoint, the one we
> have today?

We have no intention to change that.

But we surely could provide separate entry points as an extra to avoid a
bunch of conditionals.