In <[EMAIL PROTECTED]>, Michael Vince <[EMAIL PROTECTED]> typed: > Nicole Harrington wrote: > > Using FreeBSD, what is really the difference, besides > >power and ability to shove in more memory, between > >having the two seperate CPUS's? > Dual core or Quad Core CPUs performance are far better compared to more > socket CPUs since they get shared access to memory cache and reduce > memory latency/probing over AMDs hypertransport bus.
Of course, it's not really that simple. For one thing, the intel quad core CPUS are two dual core chips in one package, and the two chips don't share internal resources - like cache. So any data in cache is only available to two of the four cpus; if the one of the other two cpus needs that data it'll have to go to the external bus. The AMD quad core package is similar - except they don't put the two chips in the same package, but provide a proprietary high-speed interconnect between them. Also, shared access to the memory cache means - well shared access to the memory cache and the memory behind it. Shared access raises the possibility of contention, which will slow things down. If all four CPUs get a cache miss for different data at the same time, one of them is in for a long wait. Yeah, this isn't very likely under most loads. How likely is it under yours? 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. <mike -- Mike Meyer <[EMAIL PROTECTED]> http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information. _______________________________________________ email@example.com mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"