Re: [PATCH] Don't export sched_mc_power_savings in laptops

[Mahesh Jagannath Salgaonkar]

Ingo Molnar wrote:
> * Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx> wrote:
>
>   
> >         Fix to prevent sched_mc_power_saving from being exported through sysfs
> >         for multicore single socket (Laptop).
> >     
> >         CPU core map of the boot cpu should be equal to possible number
> >         of cpus for single socket system.
> >     
> >         This fix has been developed at FOSS.in kernel workout.
> >     
> >         Signed-off-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>
> >
> > diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> > index 4850e4b..4adc830 100644
> > --- a/arch/x86/include/asm/topology.h
> > +++ b/arch/x86/include/asm/topology.h
> > @@ -239,7 +239,7 @@ struct pci_bus;
> >  void set_pci_bus_resources_arch_default(struct pci_bus *b);
> >  
> >  #ifdef CONFIG_SMP
> > -#define mc_capable()			(boot_cpu_data.x86_max_cores > 1)
> > +#define mc_capable()	(cpus_weight(per_cpu(cpu_core_map,0)) != nr_cpu_ids)
> >     
>
> hm, dunno. sched_mc_power_savings should have no effect on single-socket 
> systems, right? So the knob should have no effect.
>
> 	Ingo
>   
Hi Ingo,

Yes, it will not have any effect but it enables additional code path 
leading to an
overhead in case of single-socket system. This overhead is only if
"sched_mc_power_savings = 1", however we are still leaving it to zero 
(default) and
preventing user space from turning it on by mistake.

Thanks,
-Mahesh.


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