Date: Mon, 20 Sep 2010 17:41:50 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-performance@freebsd.org Subject: Re: Intel TurboBoost in practice Message-ID: <i77vbq$a00$1@dough.gmane.org> In-Reply-To: <4C959830.3060808@FreeBSD.org> References: <4C4AF046.40507@FreeBSD.org> <4C959830.3060808@FreeBSD.org>
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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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