linux-kernel - Re: [PATCH v3 1/2] x86, tsc: Fallback to normal calibration if fast MSR calibration fails

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Message-ID: <20140209142048.GA28126@gmail.com>
Date:	Sun, 9 Feb 2014 15:20:48 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Bin Gao <bin.gao@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH v3 1/2] x86, tsc: Fallback to normal calibration if fast
 MSR calibration fails


* Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:

> On Thu, Feb 06, 2014 at 03:34:18PM +0100, Thomas Gleixner wrote:
> > On Thu, 6 Feb 2014, Mika Westerberg wrote:
> > >  arch/x86/kernel/tsc.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> > > index 19e5adb49a27..56facfc54575 100644
> > > --- a/arch/x86/kernel/tsc.c
> > > +++ b/arch/x86/kernel/tsc.c
> > > @@ -655,10 +655,11 @@ unsigned long native_calibrate_tsc(void)
> > >  	local_irq_save(flags);
> > >  	i = try_msr_calibrate_tsc(&fast_calibrate);
> > >  	local_irq_restore(flags);
> > > -	if (i >= 0) {
> > > -		if (i == 0)
> > > -			pr_warn("Fast TSC calibration using MSR failed\n");
> > > +	if (i > 0) {
> > >  		return fast_calibrate;
> > > +	} else if (i == 0) {
> > > +		pr_warn("Fast TSC calibration using MSR failed\n");
> > > +		/* Continue with the normal calibration */
> > >  	}
> > 
> > Bah. Can we please fix that proper. The whole 0,1,-1 return value from
> > try_msr_calibrate_tsc() is just horrible. Why not doing the obvious?
> 
> Yes, that looks better and works fine, thanks.
> 
> Tested-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

Please resend the two updated/fixed patches in a new thread.

Thanks,

	Ingo
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