Intel TurboBoost in practice
rpaulo at lavabit.com
Sat Jul 24 18:20:04 UTC 2010
On 24 Jul 2010, at 14:53, Alexander Motin wrote:
> 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
> 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?
> PPS: I expect even better effect achieved by further reducing interrupt
> rates on idle CPUs.
> Alexander Motin
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