Date: Thu, 8 Feb 2007 11:49:01 -0500 From: Mike Meyer <mwm-keyword-freebsdquestions.8c5a2e@mired.org> To: Cy Schubert <Cy.Schubert@komquats.com> Cc: freebsd-questions@freebsd.org, freebsd-amd64@freebsd.org Subject: Re: Dual Core Or Dual CPU - What's the real difference in performance? Message-ID: <17867.21629.224092.189457@bhuda.mired.org> In-Reply-To: <200702081518.l18FIeMR002991@cwsys.cwsent.com> References: <mwm@mired.org> <17866.47828.219523.71972@bhuda.mired.org> <200702081518.l18FIeMR002991@cwsys.cwsent.com>
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In <200702081518.l18FIeMR002991@cwsys.cwsent.com>, Cy Schubert <Cy.Schubert@komquats.com> typed: > In message <17866.47828.219523.71972@bhuda.mired.org>, Mike Meyer writes: > > Generally, more processors means things will go faster until you run > > out of threads. However, if there's some shared resource that is the > > bottleneck for your load, and the resource doesn't support > > simultaneous access by all the cores, more cores can slow things > > down. > > > > Of course, it's not really that simple. Some shared resources can be > > managed so as to make things improve under most loads, even if they > > don't support simultaneous access. > > Generally speaking the performance increase is not linear. At some point > there is no benefit to adding more processors. When some other resources becomes the bottleneck. Which resource depends on the workload. In some cases, adding processors will slow things down. > To add another dimension to this discussion, hyperthreading uses spare > cycles in a single processor to pretend there are two processors, > increasing performance for some apps and reducing performance for other > apps. I think hyperthreading gets a bad rap. It shares lots of resources - like the computing units - so there are lots of workloads that cause things to get worse when you add a processor. But the general case should still be that it gets faster. > Generally speaking, dual core is an inexpensive way to get SMP into the > hands of people who could not normally afford SMP technology as it was. Gee, I thought it was a reaction to losing the clock rate war. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information.
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