linux-kernel - RE: [PATCH 3/8] x86/apic: allow use of lapic timer early calibration result

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Date:	Tue, 11 May 2010 21:50:10 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Pan, Jacob jun" <jacob.jun.pan@...el.com>
cc:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	"Du, Alek" <alek.du@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"Tang, Feng" <feng.tang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 3/8] x86/apic: allow use of lapic timer early calibration
 result

Jacob,

On Tue, 11 May 2010, Pan, Jacob jun wrote:

> Thanks for the review.
> 
> > >
> > > lapic timer calibration can be combined with tsc in platform specific
> > > calibration functions. if such calibration result is obtained early,
> > > we can skip the redundent calibration loops.
> > 
> > I'd rather move lapic calibration into TSC calibration in general as
> > we do the same thing twice for no good reason.
> > 
> > That needs some code restructuring, but that's worth it.
> > 
> I am trying to avoid the risks of completely remove the current lapic 
> calibration code since there are so many platforms with different timer
> options. And I don't understand things like why pm timer is preferred.
> Why not use the rating in clocksource?

We do not have access to the clocksource at that point. But we do a
calibration loop for TSC and for lapic timer. There is no reason why
we can't do that in one go.
 
> > Aside of my general objection it'd be not a good idea to make this
> > global w/o renaming it to something sensible like
> > lapic_timer_frequency.
> > 
> perhaps, the calibration data can directly be assigned to lapic timer
> clock_event_device.mult? There is no need for the device specific result
> scale (e.g. bus clocks per tick)

No. That needs an accessor function.

Thanks,

	tglx
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