Intel TurboBoost in practice

Garrett Cooper gcooper at
Sat Jul 24 19:16:20 UTC 2010

On Sat, Jul 24, 2010 at 9:18 AM, Rui Paulo <rpaulo at> wrote:
> On 24 Jul 2010, at 14:53, Alexander Motin wrote:
>> Hi.
>> I've make small observations of Intel TurboBoost technology under
>> FreeBSD. This technology allows Intel Core i5/i7 CPUs to rise frequency
>> of some cores if other cores are idle and power/thermal conditions
>> permit. CPU core counted as idle, if it has been put into C3 or deeper
>> power state (may reflect ACPI C2/C3 states). So to reach maximal
>> effectiveness, some tuning may be needed.
>> Here is my test case: FreeBSD 9-CURRENT on Core i5 650 CPU, 3.2GHz + 1/2
>> TurboBoost steps (+133/+266MHz) with boxed cooler at the open air. I was
>> measuring building time of the net/mpd5 from sources, using only one CPU
>> core (cpuset -l 0 time make).
>> Untuned system (hz=1000):     14.15 sec
>> Enabled ACPI C2 (hz=1000+C2): 13.85 sec
>> Enabled ACPI C3 (hz=1000+C3): 13.91 sec
>> Reduced HZ (hz=100):          14.16 sec
>> Enabled ACPI C2 (hz=100+C2):  13.85 sec
>> Enabled ACPI C3 (hz=100+C3):  13.86 sec
>> Timers tuned* (hz=100):       14.10 sec
>> Enabled ACPI C2 (hz=100+C2):  13.71 sec
>> Enabled ACPI C3 (hz=100+C3):  13.73 sec
>> All numbers tested few times and are repeatable up to +/-0.01sec.
>> *) Timers were tuned to reduce interrupt rates and respectively increase
>> idle cores sleep time. These lines were added to loader.conf:
>> sysctl kern.eventtimer.timer1=i8254
>> sysctl kern.eventtimer.timer2=NONE
>> kern.eventtimer.singlemul=1
>> kern.hz="100"
>> PS: In this case benefit is small, but it is the least that can be
>> achieved, depending on CPU model. Some models allow frequency to be
>> risen by up to 6 steps (+798MHz).
> The numbers that you are showing doesn't show much difference. Have you tried buildworld?

Agreed. The numbers are small enough that there could be a large
degree of variation just based on environmental factors alone; there
are other things that go into that as well, such as disk I/O, etc,
that probably shouldn't be factored into a CPU performance test.


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