Re: need help making shell script use two CPUs/cores
Stan Hoeppner <stan@hardwarefreak.com> writes:
> Carl Johnson put forth on 1/13/2011 11:34 AM:
>
>> Processors Time (seconds)
>> P1 66
>> P2 36
>> P3 25
>> P4 20
>> P5 20
>> P6 20
>> P7 20
>> P8 20
>
> Your numbers bear out exactly what I predicted. Look at the decrease in run
> time from 1 to 2, 2 to 3, and from 3 to 4 processes:
>
> #CPUs Decremental run time Fractional gain per CPU
> 2 30s 1/2
> 3 11s 1/6th
> 4 5s 1/13th
>
> You can clearly see the effects of serious memory contention when 3 cores are
> pegged. Bringing the 4th core into the mix yields almost nothing compared to
> three cores, cutting only 5 seconds from a 66 second run time.
I seem to be looking at it in a different way, because the numbers don't
seem that much different that what I would expect.
#CPUs time theoretical time-theoretical gain/CPU(theoretical)
1 66
2 36 66/2 = 33 36-33 = 3 (+9%) 1 -1/2 = 1/2
3 25 66/3 = 22 25-22 = 3 (+14%) 1/2-1/3 = 1/6
4 20 66/4 = 16.5 20-16.5 = 3.5 (+21%) 1/3-1/4 = 1/12
--
Carl Johnson carlj@peak.org
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