linux-kernel - Re: [PATCH v2] x86/tsc: Set X86_FEATURE_TSC

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Date:   Wed, 12 Oct 2016 09:52:34 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bin Gao <bin.gao@...ux.intel.com>
cc:     Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
        John Stultz <john.stultz@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, bin.gao@...el.com
Subject: Re: [PATCH v2] x86/tsc: Set X86_FEATURE_TSC_RELIABLE to skip refined
 calibration

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
wrote:

> > 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

Thanks,

	tglx