Improved Intel Turbo Boost status/control

Alexander Motin mav at
Mon Mar 12 19:15:41 UTC 2012


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 

ACPI reports extra performance level with frequency 1MHz above the 
nominal to control Intel Turbo Boost operation. It is not a bug, but 
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
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

Alexander Motin

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