Re: writing a cpufreq driver

[Bruno Ducrot <ducrot@poupinou.org>]

On Thu, Sep 21, 2006 at 03:47:14PM -0400, Dave Jones wrote:
> On Thu, Sep 21, 2006 at 02:38:22PM -0500, Langsdorf, Mark wrote:
>  > >  > 1.  The first time cpufreq changes speed, I get the whole 
>  > > "Losing some
>  > >  > ticks... checking if CPU frequency changed." then 
>  > > eventually "Losing too
>  > >  > many ticks!" and timer switches to PIT.  This does not 
>  > > happen when I use
>  > >  > the /dev/toshiba driver to change speeds from userspace.  
>  > > Not sure what
>  > >  > is going on here...  SMI handler latency is between 6 and 7 ms.
>  > > 
>  > > Is loops_per_jiffy being correctly scaled on a speed transition?
>  > > Hmm, powernow-k7.c seems to be the only driver that's calling 
>  > > recalibrate_cpu_khz()
>  > 
>  > Do drivers need to be doing that?  I would have thought the
>  > time could would do it after receiving the notification.
> 
> Looking at it again..
> cpufreq_notify_transition() is calling adjust_jiffies()
> which should be doing the same thing, so we should be good to go.
> 
> It looks like feasible that recalibrate_cpu_khz() could actually
> be killed off.

It's called only at init time because cpu_khz is not
reliable on some platform due to braindamaged BIOS
that switch frequency of the K7 onto the SMM handler
when ACPI enable performance control, breaking AMD
recommandation at the same time BTW.

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.