linux-kernel - Re: [PATCH] x86, apic: Add apic calibration hook.

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Date:	Tue, 24 Aug 2010 14:58:10 -0700
From:	Alok Kataria <akataria@...are.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, apic: Add apic calibration hook.


On Tue, 2010-08-24 at 14:51 -0700, Thomas Gleixner wrote:
> Alok,
> 
> On Tue, 24 Aug 2010, Alok Kataria wrote:
> 
> > Hi Thomas,
> > 
> > Thanks for taking a look.
> > 
> > On Tue, 2010-08-24 at 06:37 -0700, Thomas Gleixner wrote:
> > > On Wed, 18 Aug 2010, Alok Kataria wrote:
> > > >  
> > > > +static void __init initialize_lapic_clkevt(long delta)
> > > > +{
> > > > +	/* Calculate the scaled math multiplication factor */
> > > > +	lapic_clockevent.mult = div_sc(delta, TICK_NSEC * LAPIC_CAL_LOOPS,
> > > > +				       lapic_clockevent.shift);
> > > > +	lapic_clockevent.max_delta_ns =
> > > > +		clockevent_delta2ns(0x7FFFFF, &lapic_clockevent);
> > > > +	lapic_clockevent.min_delta_ns =
> > > > +		clockevent_delta2ns(0xF, &lapic_clockevent);
> > > > +}
> > > > +
> > > >  static int __init calibrate_APIC_clock(void)
> > > >  {
> > > > +	apic_calibration_res = x86_init.timers.calibrate_apic();
> > > > +	if (apic_calibration_res) {
> > > > +		struct clock_event_device *levt = &__get_cpu_var(lapic_events);
> > > > +		long delta;
> > > > +
> > > > +		if (lapic_clockevent.mult)
> > > > +			return 0;
> > > 
> > >   Why is this necessary ? calibrate_APIC_clock() is only called once.
> > > 
> > 
> > Yes, though timer.calibrate_apci() could behave differently on different
> > platforms. For eg. the vmware_calibrate_apic doesn't initialize any of
> > the lapic_clockevent state and we need this to set it up in that case.
> 
> Can we please make this consistent ?

Let me rework this patch and get back in a day or two.

Thanks,
Alok
> 
> Thanks,
> 
> 	tglx

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