Messages in this thread | | | Date | Sat, 19 Sep 2009 14:11:38 +0300 | From | Avi Kivity <> | Subject | Re: efficient access to "rotational"; new fcntl? |
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On 09/19/2009 12:19 PM, Arjan van de Ven wrote: >> However, sort *would* benefit, and some UCLA students implemented that >> for a term project. Unfortunately, the project is stalled because the >> implementation was not efficient enough, and no one has found the >> time to improve it since. >> > parallel sort... call me skeptical. My gut feeling is that you'll get > killed by communication overhead. > (sort seems to be more communication than raw cpu use) > >
Why? a sort that fits in memory is purely cpu and memory access.
Instead of O(N log N) you'd get K * O(N/K log N/K) followed by an O(N) merge. For large N and small K, you get a speedup of roughly K (since the O(N) merge is dominated by the preceding sort.
-- Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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