Re: [PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag

[Thomas Gleixner]

On Fri, 21 Oct 2016, Peter Zijlstra wrote:
> On Thu, Oct 20, 2016 at 09:37:50PM +0200, Thomas Gleixner wrote:
> 
> > Well, we have the same issue on other platforms/models which set the
> > reliable flag.
> 
> I was not aware we had other platforms doing this, git grep tells me
> intel-mid does this as well..
> 
> > So one sanity check we can do is to read the IA32_TSC_ADJUST MSR on all
> > cores. They should all have the same value (usually 0) or at least have a
> > very minimal delta. If that's off by more than 1us then something is fishy
> > especially on single socket systems. We could at least WARN about it.
> > 
> > We could do this in idle occasionally as well, so we can detect the dreaded
> > "SMI wants to hide the cycles" crapola.
> 
> Indeed, that sounds like the best we can; and probably should; do.

I'll have a look at that in the next days.

Thanks,

	tglx