[GE users] scheduling questions

Reuti reuti at staff.uni-marburg.de
Thu Jan 12 23:41:04 GMT 2006


Hi,

Am 12.01.2006 um 16:44 schrieb Richard Smith:

> Hi
>
> 1. Will SGE chose faster nodes over slower nodes automatically, or  
> do I have to configure this behaviour? (E.g. put faster nodes into  
> a different queue?)  So far it appears to be doing this, but I  
> wonder if it is just a side effect of the fast nodes appearing at  
> the top of the hostgroup.
>

as Chris mentioned, I would use a setup to sort the queue instances  
by sequence number and have a lower one for the faster nodes.

> 2. When the system load is over a certain value, I understand SGE  
> will not schedule jobs on a node.  How do I change this value (or  
> disable this check completely)?  I don't want CPUs sitting idle  
> because the system load happens to have gone slightly too high a  
> few minutes previously.
>

This is just the entry: load_thresholds in the queue definition,  
which you can set to NONE to disable this behavior.

Opinions are different about this of course, and my personal is:

- that it's mostly useful for a large SMP machine with 64 or so CPU  
to use np_load_avg. With some parallel applications not running in  
parallel all the time, it might be possible to have 128 slots on this  
machine, and throw jobs on it until the average load of 1.75 is reached.

- If you have just slots equal to CPUs, there also shouldn't be a  
need for this limit at all.

- We have dual CPU machines, and use a setup of 2 parallel slots  
(nice 0) and 2 serial slots (nice 19) per node. The idea is to use  
the CPU time while some parallel applications are just in a step  
where it's not doing much parallel work. So, the load is 4 on the  
nodes, and it's the intended setup this way (load is just the numer  
of processes eligible to run besides the one in D-state on Linux).

Therefore I also disabled this in our cluster. - Reuti

> Thanks.
>
> -- 
> Richard
>
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