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

    Thanks,
    -Mahesh.




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