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    SubjectRe: [PATCH] mechanism to disable built in cpu frequency drivers/governors. (v1)
    >>> On 14.03.12 at 00:18, Konrad Rzeszutek Wilk <> wrote:
    > The purpose of these patches is two-fold:
    > 1) Remove weird performance issues encountered in the field where the
    > Linux kernel cpufreq scaling drivers would change the P-states while the
    > Xen hypervisor would do the same.
    > 2) Provide a runtime knob from within the kernel to disable the cpu
    > frequency
    > API (akin to the behavior of "#CONFIG_CPU_CPUFREQ is not set").

    Acked-by: Jan Beulich <>

    (Albeit I'd recommend using 'bool' for the variable and function return
    types in the first patch.)

    > The patches are based on the mechanism that Len Brown came up for the
    > cpuidle
    > drivers - where there is a disable_cpuidle() call. His patches also provided
    > a module parameter - but I wasn't sure whether that is something you would
    > want.
    > (for reference, Len's patch is d91ee5863b71e8c90eaf6035bff3078a85e2e7b5)
    > The other way of disabling the cpufreq scaling drivers from being invoked
    > is by thwarting the cpufreq drivers from loading by influencing their
    > startup
    > checks. For powernow-k8 that is easy - disallow the RDMSR (and that is
    > currently
    > happening). For acpi-cpufreq I am not sure what could be done - the calls it
    > makes are to the ACPI libraries which we need for other uses.
    > Another solution I thought off was to provide a cpufreq governor that would
    > be a nop, and hence end up not calling the cpufreq scaling drivers. But that
    > just seems heavy-handed and I am not sure how the decision of when to load it
    > (and set it) would be done.
    > arch/x86/xen/setup.c | 1 +
    > drivers/cpufreq/cpufreq.c | 24 ++++++++++++++++++++++++
    > include/linux/cpufreq.h | 2 ++
    > 3 files changed, 27 insertions(+), 0 deletions(-)

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