Date: Mon, 12 Apr 2010 20:16:18 -0400 From: Michael Poole <mdpoole@troilus.org> To: Maho NAKATA <chat95@mac.com> Cc: adrian@freebsd.org, freebsd-stable@freebsd.org Subject: Re: Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920 Message-ID: <87mxx8gqb1.fsf@troilus.org> In-Reply-To: <20100413.082856.690091871650385955.chat95@mac.com> (Maho NAKATA's message of "Tue, 13 Apr 2010 08:28:56 %2B0900 (JST)") References: <t2ud763ac661004120231q44e9a4f7z5c0f11a31725deb@mail.gmail.com> <h2yea2d4a5b1004120658xba353f17w894d33e08558f3ea@mail.gmail.com> <87tyrghiio.fsf@troilus.org> <20100413.082856.690091871650385955.chat95@mac.com>
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Maho NAKATA writes: > From: Michael Poole <mdpoole@troilus.org> > Subject: Re: Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920 > Date: Mon, 12 Apr 2010 10:06:55 -0400 > >> Nakata-san's theoretical performance numbers assume 4 to 4.2 operations >> per core per cycle at the nominal (2.66 GHz, non-TurboBoost) clock rate. >> (DGEMM is double precision, but I am not familiar enough with scientific >> computing or with the Nehalem implementation of SSE to know why it is >> four operations per cycle rather than two -- is it because double >> precision counts as two FLOPs or is it because of multiple issue?) >> TurboBoost runs up to 2.93 GHz on this CPU, so it doesn't fit either the >> theoretical peak performance or the performance discrepancy very well. > > Hi Michael, > I read http://www.intel.com/support/processors/sb/cs-023143.htm > and TurboBoost on 920 is 2.80GHz. Ah. I was looking at http://ark.intel.com/Product.aspx?id=37147 . Given a 2.80 GHz TurboBoost, the 44.8 GFLOPS theoretical performance number makes sense. I think the more important point is that TurboBoost on this CPU gives at most a 10% speedup, so it cannot explain the 25% performance difference. Michael
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