[GE users] Does oversubscribing nodes actually hurt anything?

Tobias Sargeant sargeant at wehi.edu.au
Thu Feb 17 01:10:02 GMT 2005


On 17/02/2005, at 10:20 AM, Reuti wrote:

> You can't damage anything by oversubscribing. When the load is above 
> 1, it will
> simply share the CPU-time with all the tasks. If we neglect the limit 
> of the
> memory/IO bandwidth, it should be the same time in total running 5 
> jobs one
> after the other on a single CPU, or let them running all at once. 
> Because of
> the mentioned limits, running all at once maybe slower, depending on 
> the type
> of application. E.g. for determine the maximum power consumption of 
> the nodes
> for our UPS, I measured one node idling and with full load. It can't 
> get
> higher.

In terms of performance, even if you have the memory/IO bandwidth to go 
round,
more than one process per CPU - especially if those processes are 
executing
different code - may induce cache thrashing, as well as some context 
switching
overhead. The extent to which this affects you will depend on various 
factors
including the type of process, the relative speeds of cache and main 
memory
and the scheduling quantum used by the operating system.

Toby.


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