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

* Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com> wrote:

> Ingo Molnar wrote:
>> * Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com> 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@linux.vnet.ibm.com>
>>>
>>> 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.

okay, makes sense - i've applied it to tip/sched/urgent (for v2.6.28
merge), thanks Mahesh!

Ingo


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