[Beowulf] scheduler policy design

Reuti reuti at staff.uni-marburg.de
Wed Apr 25 02:21:35 PDT 2007

Am 24.04.2007 um 14:30 schrieb Toon Knapen:

> Tim Cutts wrote:
>>> but what if you have a bi-cpu bi-core machine to which you assign  
>>> 4 slots. Now one slot is being used by a process which performs  
>>> heavy IO. Suppose another process is launched that performs heavy  
>>> IO. In that case the latter process should wait until the first  
>>> one is done to avoid slowing down the efficiency of the system.  
>>> Generally however, clusters take only time and memory  
>>> requirements into account.
>> I think that varies.  LSF records the current I/O of a node as one  
>> of its load indices, so you can request a node which is doing less  
>> than a certain amount of I/O.  I imagine the same is true of SGE,  
>> but I wouldn't know.
> Indeed, using SGE you could also take this into account. However if  
> someone submits 4 jobs, the jobs do not directly start to generate  
> heavy I/O. So the scheduler might think that the 4 jobs can easily  
> coexist on this same node. However, after a few minutes all 4 jobs  
> start eating disk BW and slow the node down horribly. What would  
> your suggestion be to solve this ?

In SGE it's possible to put some "job_load_adjustments" with  
"load_adjustment_decay_time" to take this into account. This will  
show some virtual load (not necessarily the CPU load) during the  
first minutes of the job. Only odd thing would be, if they were  
scheduled in the same cycle to the same node.

-- Reuti

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