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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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