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Message Posted: Wed, 21 Mar 2007 @ 22:05:41 GMT

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Subj:   Re: Maximum amount of CPU allowed
From:   Morhart, Allan

The theoretical maximum number of CPU seconds per hour is :

     (#CPUs per node) * (#nodes) * (3600 seconds per hour) * 0.8

This is true regardless of node model number.

So if you have 10x5400 nodes then you get

(4 CPUs per node) * (10 nodes) * (3600 seconds per hour) * 0.8 = 115200 CPU seconds per hour.

And if you have 10x5450 nodes then you still get

(4 CPUs per node) * (10 nodes) * (3600 seconds per hour) * 0.8 = 115200 CPU seconds per hour.


- We use 0.8 as a factor because this assumes approximately 20% overhead is eaten up by the Unix OS, your mileage may vary.

- A 5400 has 2 physical CPUs and 4 logical CPUs, Resusage sees it as 4 CPUs, so we consider this to be 4 CPUs per node

- Depending on what you are doing with the calculations, a 5450 CPU second has a heavier weighting (does more work) than a 5400 CPU second

- If you have a hybrid system made up more than one HW generation, you have to adjust for the difference in CPU chip power (good luck!)

- In dbc.ampusage, depending on your Account String settings, all CPU seconds are logged against the starting period of when the query began. So even if the query ran for 3 days, all the CPU seconds will be logged against the starting period (3 days ago). So it is possible to get numbers larger than the theoretical maximum in any given period.

hope this helps


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