Re: [PATCH v4 3/7] acpi-cpufreq: Add support for disabling dynamicoverclocking

From: Andy Lutomirski
Date: Sat Jul 23 2011 - 23:15:26 EST

On 07/18/2011 12:37 PM, Matthew Garrett wrote:
One feature present in powernow-k8 that isn't present in acpi-cpufreq is
support for enabling or disabling AMD's core performance boost technology.
This patch adds that support to acpi-cpufreq, but also extends it to allow
Intel's dynamic acceleration to be disabled via the same interface. The
sysfs entry retains the cpb name for compatibility purposes.

Signed-off-by: Matthew Garrett<mjg@xxxxxxxxxx>
drivers/cpufreq/acpi-cpufreq.c | 191 ++++++++++++++++++++++++++++++++++++++++
1 files changed, 191 insertions(+), 0 deletions(-)

+ if (enable)
+ else
+ }

I was curious and looked it up. Intel SDM volume 3, says:

Opportunistic processor performance operation can be disabled by setting bit 38 of
IA32_MISC_ENABLE. This mechanism is intended for BIOS only. If
IA32_MISC_ENABLE[38] is set, CPUID.06H:EAX[1] will return 0.

and the next section says:

System software can temporarily disengage opportunistic processor performance
operation by setting bit 32 of the IA32_PERF_CTL MSR (0199H), using a read-
modify-write sequence on the MSR.

Would that be a better way to control boost mode on Intel chips?

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