[Beowulf] Strange SGE scheduling problem

Shannon V. Davidson svdavidson at charter.net
Fri Jul 25 12:22:45 EDT 2008


Schoenefeld, Keith wrote:
> This definitely looked promising, but unfortunately it didn't work.  I
> both added the appropriate export lines to my qsub file, and then when
> that didn't work I checked the mvapich.conf file and confirmed that the
> processor affinity was disabled.  I wonder if I can turn it on and make
> it work, but unfortunately the cluster is full at the moment, so I can't
> test it.
>   

You may want to verify that the environment variable was actually passed 
down to the MPI task.  To set environment variables for MPI jobs, I 
usually either specify the environment variable on the mpirun command 
line or in a wrapper script:

   mpirun -np 32 -hostfile nodes  VIADEV_ENABLE_AFFINITY=0 a.out

   mpirun -np 32 -hostfile nodes run.sh a.out

       where run.sh sets up the local environment including environment 
variables.

The second method is more portable to various shells and MPI versions.

Shannon

> -- KS
>
> -----Original Message-----
> From: Shannon V. Davidson [mailto:svdavidson at charter.net] 
> Sent: Wednesday, July 23, 2008 4:02 PM
> To: Schoenefeld, Keith
> Cc: beowulf at beowulf.org
> Subject: Re: [Beowulf] Strange SGE scheduling problem
>
> Schoenefeld, Keith wrote:
>   
>> My cluster has 8 slots (cores)/node in the form of two quad-core
>> processors. Only recently we've started running jobs on it that
>>     
> require
>   
>> 12 slots.  We've noticed significant speed problems running multiple
>>     
> 12
>   
>> slot jobs, and quickly discovered that the node that was running 4
>>     
> slots
>   
>> on one job and 4 slots on another job was running both jobs on the
>>     
> same
>   
>> processor cores (i.e. both job1 and job2 were running on CPU's #0-#3,
>> and the CPUs #4-#7 were left idling.  The result is that the jobs were
>> competing for time on half the processors that were available.
>>
>> In addition, a 4 slot job started well after the 12 slot job has
>>     
> ramped
>   
>> up results in the same problem (both the 12 slot job and the four slot
>> job get assigned to the same slots on a given node).
>>
>> Any insight as to what is occurring here and how I could prevent it
>>     
> from
>   
>> happening?  We were are using SGE + mvapich 1.0 and a PE that has the
>> $fill_up allocation rule.
>>
>> I have also posted this question to the hpc_training-l at georgetown.edu
>> mailing list, so my apologies for people who get this email multiple
>> times.
>> Any insight as to what is occurring here and how I could prevent it
>>     
> from
>   
>> happening?  We were are using SGE + mvapich 1.0 and a PE that has the
>> $fill_up allocation rule.
>>   
>>     
>
> This sounds like MVAPICH is assigning your MPI tasks to your CPUs 
> starting with CPU#0.  If you are going to run multiple MVAPICH jobs on 
> the same host, turn off CPU affinity by starting the MPI tasks with the 
> environment variable VIADEV_USE_AFFINITY=0 and VIADEV_ENABLE_AFFINITY=0.
>
> Cheers,
> Shannon
>
>   
>> Any help is appreciated.
>>
>> -- KS
>>
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>   
>>   
>>     
>
>   

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