Re: [patch 09/11] x86/vdso: Simplify the invalid vclock case

[Thomas Gleixner]

On Tue, 18 Sep 2018, Thomas Gleixner wrote:
> On Tue, 18 Sep 2018, Peter Zijlstra wrote:
> > > Your memory serves you right. That's indeed observable on CPUs which
> > > lack TSC_ADJUST.
> > 
> > But, if the gtod code can observe this, then why doesn't the code that
> > checks the sync?
> 
> Because it depends where the involved CPUs are in the topology. The sync
> code might just run on the same package an simply not see it. Yes, w/o
> TSC_ADJUST the TSC sync code can just fail to see the havoc.

Even with TSC adjust the TSC can be slightly off by design on multi-socket
systems.

Thanks,

	tglx