Messages in this thread | | | Date | Tue, 30 Mar 2010 23:22:21 -0400 | From | Andrew Morton <> | Subject | Re: [-v2 PATCH 2/6] powernow-k8: Add core performance boost support |
| |
On Wed, 31 Mar 2010 08:13:43 +0200 Borislav Petkov <bp@amd64.org> 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.
| |