Re: [PATCH v2] x86/tsc: Set X86_FEATURE_TSC_RELIABLE to skip refined calibration

From: Thomas Gleixner
Date: Wed Oct 12 2016 - 03:56:51 EST

On Tue, 11 Oct 2016, Bin Gao wrote:
> On Fri, Aug 26, 2016 at 12:14:58PM +0200, Thomas Gleixner wrote:
> The Linux kernel does think a reliable calibration implies the reliability (i.e.
> no watchdog required). I'm posting some code pieces to explain.

I know that and I know exactly how all that works. And I certainly did not
ask for an explanation of the current state of affairs. Here is what I

> > Second thoughts. We should seperate the calibration aspect from the reliablity
> > aspect.
> >
> > If a MSR/CPUID readout provides reliable calibration then this does not tell
> > us about the reliablity (i.e. no watchdog required). So having two flags for
> > this - and sure you can set both on those SoCs is the proper solution.

In other words: I want to have two seperate flags:

1) FEATURE_KNOWN_FREQUENCY - Grab the frequency from CPUID/MSR or whatever
and skip the whole calibration thing

2) FEATURE_RELIABLE - Do not invoke the watchdog