[slurm-users] Single Node cluster. How to manage oversubscribing

Sat Feb 25 16:15:41 UTC 2023

Hi,

Declaring cores=64 will absolutely work but if you start running MPI you'll
want a more detailed config description.  The easy way to read it is "128=2
sockets * 32 corespersocket * 2 threads per core".

NodeName=hpc[306-308] CPUs=128 Sockets=2 CoresPerSocket=32 ThreadsPerCore=2
RealMemory=512000 TmpDisk=100

But if you just want to work with logical cores the "cpus=128" will work.

If you go with the more detailed description then you need to declare
oversubscription (hyperthreading) in the partition declaration.  By default
slurm will not let two different jobs share the logical cores comprising a
physical core.  For example if Sue has an Array of 1-1000 her array tasks
could each take a logical core on a physical core.  But if Jamal is also
running they would not be able to share the physical core. (as I understand
it).

PartitionName=a Nodes= [301-308] Default=No OverSubscribe=YES:2
MaxTime=Infinite State=Up AllowAccounts=cowboys

In the sbatch/srun the user needs to add a declaration "oversubscribe=yes"
telling slurm the job can run on both logical cores available.  In the days
on Knight's Landing each core could handle four logical cores but I don't
believe there are any current AMD or Intel processors supporting more then
two logical cores (hyperthreads per core).  The conversation about
hyperthreads is difficult as the Intel terminology is logical cores for
hyperthreading and cores for physical cores but the tendency is to call the
logical cores threads or hyperthreaded cores.  This can be very confusing
for consumers of the resources.

In any case, if you create an array job of 1-100 sleep jobs, my simplest
logical test job, then you can use scontrol show node <nodename> to see the
nodes resource configuration as well as consumption.  squeue -w <nodename>
-i 10 will iteratate every ten seconds to show you the node chomping
through the job.

Hope this helps.  Once you are comfortable I would urge you to use the
NodeName/Partition descriptor format above and encourage your users to
declare oversubscription in their jobs.  It is a little more work up front
but far easier than correcting scripts later.

Doug

On Thu, Feb 23, 2023 at 9:41 PM Analabha Roy <hariseldon99 at gmail.com> wrote:

> Howdy, and thanks for the warm welcome,
>
> On Fri, 24 Feb 2023 at 07:31, Doug Meyer <dameyer99 at gmail.com> wrote:
>
>> Hi,
>>
>> Did you configure your node definition with the outputs of slurmd -C?
>> Ignore boards.  Don't know if it is still true but several years ago
>> declaring boards made things difficult.
>>
>>
> $ slurmd -C
> NodeName=shavak-DIT400TR-55L CPUs=64 Boards=1 SocketsPerBoard=2
> CoresPerSocket=16 ThreadsPerCore=2 RealMemory=95311
> UpTime=0-00:47:51
> $ grep NodeName /etc/slurm-llnl/slurm.conf
> NodeName=shavak-DIT400TR-55L CPUs=64 RealMemory=95311 Gres=gpu:1
>
> There is a difference. I, too, discarded the Boards and sockets in
> slurmd.conf . Is that the problem?
>
>
>
>
>
>
>
>> Also, if you have hyperthreaded AMD or Intel processors your partition
>> declaration should be overscribe:2
>>
>>
> Yes I do, It's actually 16 X 2 cores with hyperthreading, but the BIOS is
> set to show them as 64 cores.
>
>
>
>
>> Start with a very simple job with a script containing sleep 100 or
>> something else without any runtime issues.
>>
>>
> I ran this MPI hello world thing
> <https://github.com/hariseldon99/buparamshavak/blob/main/shavak_root/usr/local/share/examples/mpi_runs_inf/mpi_count.c>with
> this sbatch script.
> <https://github.com/hariseldon99/buparamshavak/blob/main/shavak_root/usr/local/share/examples/mpi_runs_inf/mpi_count_normal.sbatch>
> Should be the same thing as your suggestion, basically.
> Should I switch to 'srun' in the batch file?
>
> AR
>
>
>> When I started with slurm I built the sbatch one small step at a time.
>> Nodes, cores. memory, partition, mail, etc
>>
>> It sounds like your config is very close but your problem may be in the
>> submit script.
>>
>> Best of luck and welcome to slurm. It is very powerful with a huge
>> community.
>>
>> Doug
>>
>>
>>
>> On Thu, Feb 23, 2023 at 6:58 AM Analabha Roy <hariseldon99 at gmail.com>
>> wrote:
>>
>>> Hi folks,
>>>
>>> I have a single-node "cluster" running Ubuntu 20.04 LTS with the
>>> distribution packages for slurm (slurm-wlm 19.05.5)
>>> Slurm only ran one job in the node at a time with the default
>>> configuration, leaving all other jobs pending.
>>> This happened even if that one job only requested like a few cores (the
>>> node has 64 cores, and slurm.conf is configged accordingly).
>>>
>>> in slurm conf, SelectType is set to select/cons_res, and
>>> SelectTypeParameters to CR_Core. NodeName is set with CPUs=64. Path to file
>>> is referenced below.
>>>
>>> So I set OverSubscribe=FORCE in the partition config and restarted the
>>> daemons.
>>>
>>> Multiple jobs are now run concurrently, but when Slurm is
>>> oversubscribed, it is *truly* *oversubscribed*. That is to say, it runs
>>> so many jobs that there are more processes running than cores/threads.
>>> How should I config slurm so that it runs multiple jobs at once per
>>> node, but ensures that it doesn't run more processes than there are cores?
>>> Is there some TRES magic for this that I can't seem to figure out?
>>>
>>> My slurm.conf is here on github:
>>> https://github.com/hariseldon99/buparamshavak/blob/main/shavak_root/etc/slurm-llnl/slurm.conf
>>> The only gres I've set is for the GPU:
>>> https://github.com/hariseldon99/buparamshavak/blob/main/shavak_root/etc/slurm-llnl/gres.conf
>>>
>>> Thanks for your attention,
>>> Regards,
>>> AR
>>> --
>>> Analabha Roy
>>> Assistant Professor
>>> Department of Physics
>>> <http://www.buruniv.ac.in/academics/department/physics>
>>> The University of Burdwan <http://www.buruniv.ac.in/>
>>> Golapbag Campus, Barddhaman 713104
>>> West Bengal, India
>>> Emails: daneel at utexas.edu, aroy at phys.buruniv.ac.in,
>>> hariseldon99 at gmail.com
>>> Webpage: http://www.ph.utexas.edu/~daneel/
>>>
>>
>
> --
> Analabha Roy
> Assistant Professor
> Department of Physics
> <http://www.buruniv.ac.in/academics/department/physics>
> The University of Burdwan <http://www.buruniv.ac.in/>
> Golapbag Campus, Barddhaman 713104
> West Bengal, India
> Emails: daneel at utexas.edu, aroy at phys.buruniv.ac.in, hariseldon99 at gmail.com
> Webpage: http://www.ph.utexas.edu/~daneel/
>
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