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

[Mike Travis]

On 10/12/2017 4:17 AM, Thomas Gleixner wrote:
> On Thu, 5 Oct 2017, mike.travis@xxxxxxx wrote:
>
> > If the TSC has already been determined to be unstable, then checking
> > TSC ADJUST values is a waste of time and generates unnecessary error
> > messages.
> >
> > Signed-off-by: Mike Travis <mike.travis@xxxxxxx>
> > Reviewed-by: Dimitri Sivanich <dimitri.sivanich@xxxxxxx>
> > Reviewed-by: Russ Anderson <russ.anderson@xxxxxxx>
> > Reviewed-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > ---
> >   arch/x86/kernel/tsc_sync.c |    8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > --- linux.orig/arch/x86/kernel/tsc_sync.c
> > +++ linux/arch/x86/kernel/tsc_sync.c
> > @@ -38,6 +38,10 @@ void tsc_verify_tsc_adjust(bool resume)
> >   	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
> >   		return;
> >   
> > +	/* Skip unnecessary error messages if TSC already unstable */
> > +	if (check_tsc_unstable())
> > +		return;
> > +
> >   	/* Rate limit the MSR check */
> >   	if (!resume && time_before(jiffies, adj->nextcheck))
> >   		return;
> > @@ -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?

> 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?
> Thanks,
>
> 	tglx