Date: Wed, 12 Oct 2016 09:52:34 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Bin Gao <bin.gao@linux.intel.com>
cc: Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        John Stultz <john.stultz@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, bin.gao@intel.com
Subject: Re: [PATCH v2] x86/tsc: Set X86_FEATURE_TSC_RELIABLE to skip refined
 calibration
In-Reply-To: <20161011211121.GA15041@worksta>
Message-ID: <alpine.DEB.2.20.1610120948250.5032@nanos>
References: <20160816174240.GA33372@worksta> <alpine.DEB.2.20.1608241049270.5714@nanos> <20160825164350.GA245186@worksta> <alpine.DEB.2.20.1608261210090.5714@nanos> <alpine.DEB.2.20.1608261212080.5714@nanos> <20161011211121.GA15041@worksta>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1015
Lines: 32

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