Improved Intel Turbo Boost status/control

Alexander Motin mav at
Mon Mar 12 19:55:31 UTC 2012

On 03/12/12 21:33, Ivan Klymenko wrote:
> В Mon, 12 Mar 2012 21:15:35 +0200
> Alexander Motin<mav at>  пишет:
>> I'd like to note that recent r232793 change to cpufreq(4) in HEAD
>> opened simple access to the  Intel Turbo Boost status/control. I've
>> found that at least two of my desktop systems (based Nehalem and
>> SandyBridge Core i7s) with enabled Intel Turbo Boost in BIOS it is
>> not use it by default, unless powerd is enabled. And before this
>> change it was difficult to detect/fix.
>> ACPI reports extra performance level with frequency 1MHz above the
>> nominal to control Intel Turbo Boost operation. It is not a bug, but
>> feature:
>> dev.cpu.0.freq_levels: 2934/106000 2933/95000 2800/82000 ...
>> In this case value 2933 means 2.93GHz, but 2934 means 3.2-3.6GHz.
>> After boot with default settings I see:
>> dev.cpu.0.freq: 2933
>> , that means Turbo Boost is disabled.
>> Enabling powerd or just adding to rc.conf
>> performance_cpu_freq="HIGH"
>> enables Turbo Boost and adds extra 10-20% to the system performance.
>> Turbo Boost operation can be monitored in run-time via the PMC with
>> command that prints number or really executed cycles per CPU core:
>> pmcstat -s unhalted-core-cycles -w 1
> Thank you very much!
> performance_cpu_freq="HIGH"
> and as this option must be combined with state of the processor C1 C2
> C3?
> performance_cx_lowest="XX"
> economy_cx_lowest="XX"

The more CPU cores on package are sleeping and the deeper they are 
sleeping, the bigger will be boost for remaining active cores. Without 
using deeper C-states boost is usually quite small (about 100-200MHz for 
desktop chips). Enabling C-states increases it in few times.

Alexander Motin

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