RE: Industry db benchmark result on recent 2.6 kernels

[Kevin Puetz]

Linus Torvalds wrote:

> 
> 
> On Fri, 1 Apr 2005, Chen, Kenneth W wrote:
>> 
>> Paul, you definitely want to check this out on your large numa box.  I
>> booted a kernel with this patch on a 32-way numa box and it took a long
>> .... time to produce the cost matrix.
> 
> Is there anything fundamentally wrong with the notion of just initializing
> the cost matrix to something that isn't completely wrong at bootup, and
> just lettign user space fill it in?

Wouldn't getting rescheduled (and thus having another program trash the
cache on you) really mess up the data collection though? I suppose by
spawning off threads, each with a fixed affinity and SCHED_FIFO one could
hang onto the CPU to collect the data. But then it's not (a lot) different
than doing it in-kernel.
 
> Then you couple that with a program that can do so automatically (ie
> move the in-kernel heuristics into user-land), and something that can
> re-load it on demand.

This part seems sensible though :-)

> Voila - you have something potentially expensive that you run once, and
> then you have a matrix that can be edited by the sysadmin later and just
> re-loaded at each boot.. That sounds pretty optimal, especially in the
> sense that it allows the sysadmin to tweak things depending on the use of
> the box is he really wants to.
> 
> Hmm? Or am I just totally on crack?
> 
> Linus


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