On Wed, 31 Mar 2010 08:13:43 +0200 Borislav Petkov <bp@xxxxxxxxx> wrote:
> > > +static void _cpb_toggle_msrs(bool t)
> > > +{
> > > + int cpu;
> > > +
> > > + rdmsr_on_cpus(cpu_online_mask, MSR_K7_HWCR, msrs);
> > > +
> > > + for_each_cpu(cpu, cpu_online_mask) {
> > > + struct msr *reg = per_cpu_ptr(msrs, cpu);
> > > + if (t)
> > > + reg->l &= ~BIT(25);
> > > + else
> > > + reg->l |= BIT(25);
> > > + }
> > > + wrmsr_on_cpus(cpu_online_mask, MSR_K7_HWCR, msrs);
> > > +}
> >
> > What prevents cpu_online_mask from changing while this is happening?
>
> Frankly, nothing.
Sneak a get_online_cpus()/put_online_cpus() in there?
> And yes, we talked a lot about this internally, since,
> you need this bit cleared on _all_ cores for the processor to boost.
> Now, if you've offlined some of the cores, you won't be able to execute
> any code on them and thus clear this bit.
>
> However, this interface is there only for benchmarking purposes and
> stuff, i.e. normally, you shouldn't need to touch it _at_ _all_ and
> boosting will work out of the box and without user interaction.
>
> So, IMHO, hotplug notifiers won't work since you need all cores online
> at that particular moment to enable boosting. It sounds more reasonable
> to me to WARN when a core is missing from the mask that boosting cannot
> be enabled. I'll cook up something later today.
--
To unsubscribe from this list: send the line "unsubscribe cpufreq" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
