Re: [Patch] Fix the possibility of insane return value of hpet_calibrate()against SMI.

[Paul Gortmaker]

Yasunori Goto wrote:
> Sorry for late response.
>
>   
> > Yasunori Goto wrote:
> >     
> > > > I've no sense of feel for how long each calibration run would take.
> > > > Would doing it 5 times show up as a significant increase in the boot
> > > > time for those that care about boot time being as quick as possible?
> > > >         
> > > Hmm. The loop times is trade off against reliable value....
> > > Though SMI is rare interruption, I don't know how frequent
> > > hypervisor's switch is.
> > >       
> > Could you, just for testing, run the calibration five thousand times or
> > so instead of five times, and count how often you get insane values?
> > (And how much delay does such an SMI add?)
> >     
>
> I tried 50000 times. But insane value was nothing.
> I think SMI is very rare.
>
>   
> > > Each calibration of this has 1 milli second.
> > > Do you think 5 msec is too long?
> > >       
> > This shouldn't matter when booting.  Anyway, I think it's possible to
> > increase TICK_CALIBRATE without losing too much accuracy.
> >     
>
> Hmm. If the person who is trying to reduce boot time for fastboot dislikes this impact,
> then I'll try Vojtech-san's way.
>   

That probably makes sense -- if it is extremely rare, and if you get two
values that are the same (within some small delta) then you probably
are 99.99% confident that you have the right data.

Paul.

> Thanks.
>   

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