Intel TurboBoost in practice

Ivan Voras ivoras at freebsd.org
Mon Sep 20 15:56:56 UTC 2010


On 09/19/10 06:57, Alexander Motin wrote:
> Getting back to that topic I would like to share some more results. This
> time I was testing Core(TM) i7 870 @ 2.93GHz. It has 8 logical cores and
> bigger allowed TurboBoost effect. I was testing real time of net/mpd5
> port building, using single CPU. I was testing it with HZ=1000 with
> different C-states allowed and with/without kern.eventtimer.idletick
> sysctl enabled (supported by the latest event timer code in HEAD). This
> sysctl, when disabled, allows to avoid most of timer interrupts on idle
> cores, allowing them to sleep deeper.

If I understand correctly, TurboBoost is supposed to increase the 
frequency of one or a small number of cores only?

What is the physical increase in frequency on this CPU when TurboBoost 
is enabled?

> As you may see, with full timer interrupt rate TurboBoost effect (part
> of it, that enabled by some number of idle cores) is about 3-4%. CPUs
> are not sleeping long enough. But without extra interrupts on idle cores
> effect increasing to more then 10%!

Is this interpretation correct: when building with single core (-j1 
effectively), using TurboBoost with the new code is >10% faster than 
without TurboBoost?

Does it have any effect if you try using all the cores?



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