RE: Incorrect mdelay() results on Power Managed Machines x86

Grover, Andrew
2001-03-28T23:15:37Z

Sounds like the TSC makes a lousy calibration method ;-)

I know on ACPI systems you are guaranteed a PM timer running at ~3.57 Mhz.
Could udelay use that, or are there other timers that are better (maybe
without the ACPI dependency)?

Regards -- Andy

> -----Original Message-----
> From: Pavel Machek [mailto:pavel@suse.cz]
> Sent: Sunday, March 25, 2001 4:07 PM
> To: Alan Cox
> Cc: sfr@canb.auug.org.au; twoller@crystal.cirrus.com;
> linux-kernel@vger.kernel.org
> Subject: Re: Incorrect mdelay() results on Power Managed Machines x86
>
>
> Hi!
>
> > > On the ThinkPad 600E (at least), we get a Power Status
> Change APM event.
> >
> > Any reason we couldn't recalibrate the bogomips on a power
> status change,
> > at least for laptops we know appear to need it (I can make
> the DMI code look
> > for matches there..)
>
> Notice that this is not 100% solution. APM is async, and you
> might already
> did few wrong delays by the time apm event is delivered to you.
>
> Also notice that at least my toshiba goes low speed (150MHz) on
> *) batteries going low
> *) overheat
>
> It goes back to 300MHz at ac power. Another crazy thing: it
> goes down to
> 35MHz on extreme overheat -- that's factor of 10 change.
> --
> Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
> details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.
>
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