Re: [RFC PATCH v3 1/3] sched: schedule balance map foundation
From: Alex Shi
Date: Thu Feb 21 2013 - 23:46:48 EST
On 02/22/2013 12:19 PM, Michael Wang wrote:
>> > Why not seek other way to change O(n^2) to O(n)?
>> > Access 2G memory is unbelievable performance cost.
> Not access 2G memory, but (2G / 16K) memory, the sbm size is O(N).
> And please notice that on 16k cpus system, topology will be deep if NUMA
> enabled (O(log N) as Peter said), and that's really a good stage for
> this idea to perform on, we could save lot's of recursed 'for' cycles.
CPU execute part is very very fast compare to the memory access, the
'for' cycles cost is most on the memory access for many domain/groups
data, not instruction execution.
In a hot patch, several KB memory access will cause clear cpu cache
pollution then make kernel slowly.
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