Re: [Ubuntu PATCH] cpufreq: fix powernow-k8 load bug

[Pavel Machek]

Hi!

>  > > --- linux-2617-pv.orig/arch/i386/kernel/cpu/cpufreq/powernow-k8.c
>  > > +++ linux-2617-pv/arch/i386/kernel/cpu/cpufreq/powernow-k8.c
>  > > @@ -1008,7 +1008,7 @@ static int __cpuinit powernowk8_cpu_init
>  > >  		 * an UP version, and is deprecated by AMD.
>  > >  		 */
>  > >  
>  > > -		if ((num_online_cpus() != 1) || (num_possible_cpus() != 1)) {
>  > > +		if ((num_online_cpus() != 1)) {
>  > >  			printk(KERN_ERR PFX "MP systems not supported by PSB BIOS structure\n");
>  > >  			kfree(data);
>  > >  			return -ENODEV;
>  > > 
>  > 
>  > Seems wrong to me... what if I boot, then hotplug second cpu?
> 
> We only run this code if powernow_k8_cpu_init_acpi() has failed,
> which it should never do on an SMP system.
> 
> So, you get exactly the same behaviour, as expected.
> You can't support >1 CPU with PSB.
> 
> The above patch makes sure things continue to work if you run
> an SMP kernel on UP hardware.

I'm pretty sure you'll find SMP machine with broken ACPI cpufreq
(therefore cpu_init_acpi() will fail). And if user is perverse enough,
he might boot with one cpu then simulate hotplug of second one.

OTOH:

1) user is already doing perverse things at this point

and

2) machine BIOS is b0rken

...so... it is only theoretical and probably not worth fixing.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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