linux-kernel - Re: [PATCH 2/5] x86/kernel: Skip TSC test and error messages if already unstable

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Date:   Thu, 12 Oct 2017 17:22:54 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mike Travis <mike.travis@....com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Bin Gao <bin.gao@...ux.intel.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Andrew Banman <andrew.banman@....com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 2/5] x86/kernel: Skip TSC test and error messages if
 already unstable

On Thu, 12 Oct 2017, Mike Travis wrote:
> On 10/12/2017 4:17 AM, Thomas Gleixner wrote:
> > On Thu, 5 Oct 2017, mike.travis@....com wrote:
> > > @@ -89,6 +93,10 @@ bool tsc_store_and_check_tsc_adjust(bool
> > >   	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
> > >   		return false;
> > >   +	/* Skip unnecessary error messages if TSC already unstable */
> > > +	if (check_tsc_unstable())
> > > +		return false;
> > > +
> > >   	rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
> > >   	cur->bootval = bootval;
> > >   	cur->adjusted = bootval;
> > 
> > This hunk rejects and I really can't figure out against which tree that
> > would apply.
> 
> My current merge tree happens to be 4.13.0-rc1 which was the latest when I
> started this patch submission.  I can update my merge tree and reapply if need
> be?

Please send patches always against top of tree and not some random ancient
version of it.

> > Btw, there are two incarnations of tsc_store_and_check_tsc_adjust().
> > Shouldn't the !SMP variant get the same treatment?
> 
> I could add it though I'm not sure the point?  If it's only one CPU would
> TSC's being out of sync become a question?

Well, this is about TSC_ADJUST and if BIOS/SMM fiddles with TSC_ADJUST
behind the kernels back, then our timekeeping is buggered. So we better
check that.

Thanks,

	tglx