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SubjectRe: Threads FAQ entry incomplete
>>>>> "Mike" == Mike Kravetz <> writes:

Mike> Note that in the 2 and 4 CPU cases, the run queue length is
Mike> aprox 2x the number of CPUs and the scheduler seems to
Mike> perform reasonably well with respect to locking. In the 8
Mike> CPU case, the number of tasks is aprox equal to the number
Mike> of CPUs yet scheduler performance has gone downhill.

Obviously, since as the number of CPUs grow, you begin
experiencing the bottleneck of shared resources (bus, memory, I/O,
etc.) multiplexing. For a large number of processors, the performance
becomes very far from linear, i.e. the gain obtained from an extra CPU
becomes very minute. That's why massively parallel computers tend to
use separate motherboards for each CPU.

BTW, I have a question: Can the availability of dual-CPU
boards for intel and amd processors, rather then tri- or quadra-CPU
boards, be explained with the fact that the performance degrades
significantly for three or more CPUs? Or is there a technological
and/or comercial reason behind? I heard somewhere that the intel holds
some patents related with many-CPU boards...



*** Rodrigo Martins de Matos Ventura <>
*** Web page:
*** Teaching Assistant and PhD Student at ISR:
*** Instituto de Sistemas e Robotica, Polo de Lisboa
*** Instituto Superior Tecnico, Lisboa, PORTUGAL
*** PGP fingerprint = 0119 AD13 9EEE 264A 3F10 31D3 89B3 C6C4 60C6 4585
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