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

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag
Date	2016-10-21 10:10 +0200
Message-ID	<suD3Q-2RW-23@gated-at.bofh.it> (permalink)
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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

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[PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag Bin Gao <bin.gao@linux.intel.com> - 2016-10-14 01:20 +0200
  Re: [PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag Thomas Gleixner <tglx@linutronix.de> - 2016-10-20 12:10 +0200
    Re: [PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag Peter Zijlstra <peterz@infradead.org> - 2016-10-20 12:20 +0200
      Re: [PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag Thomas Gleixner <tglx@linutronix.de> - 2016-10-20 21:50 +0200
        Re: [PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag Peter Zijlstra <peterz@infradead.org> - 2016-10-21 07:50 +0200
          Re: [PATCH v3] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag Thomas Gleixner <tglx@linutronix.de> - 2016-10-21 10:10 +0200

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