At least for our cluster we generally recommend that if you are
submitting large numbers of jobs you either use a job array or you just
for loop over the jobs you want to submit. A fork bomb is definitely
not recommended. For highest throughput submission a job array is your
best bet as in one submission it will generate thousands of jobs which
then the scheduler can handle sensibly. So I highly recommend using job
arrays.
-Paul Edmon-
On 8/27/19 3:45 AM, Guillaume Perrault Archambault wrote:
Hi Paul,
Thanks a lot for your suggestion.
The cluster I'm using has thousands of users, so I'm doubtful the
admins will change this setting just for me. But I'll mention it to
the support team I'm working with.
I was hoping more for something that can be done on the user end.
Is there some way for the user to measure whether the scheduler is in
RPC saturation? And then if it is, I could make sure my script doesn't
launch too many jobs in parallel.
Sorry if my question is too vague, I don't understand the backend of
the SLURM scheduler too well, so my questions are using the limited
terminology of a user.
My concern is just to make sure that my scripts don't send out more
commands (simultaneously) than the scheduler can handle.
For example, as an extreme scenario, suppose a user forks off 1000
sbatch commands in parallel, is that more than the scheduler can
handle? As a user, how can I know whether it is?
Regards,
Guillaume.
On Mon, Aug 26, 2019 at 10:15 AM Paul Edmon <ped...@cfa.harvard.edu
<mailto:ped...@cfa.harvard.edu>> wrote:
We've hit this before due to RPC saturation. I highly recommend
using max_rpc_cnt and/or defer for scheduling. That should help
alleviate this problem.
-Paul Edmon-
On 8/26/19 2:12 AM, Guillaume Perrault Archambault wrote:
Hello,
I wrote a regression-testing toolkit to manage large numbers of
SLURM jobs and their output (the toolkit can be found here
<https://github.com/gobbedy/slurm_simulation_toolkit/> if anyone
is interested).
To make job launching faster, sbatch commands are forked, so that
numerous jobs may be submitted in parallel.
We (the cluster admin and myself) are concerned that this may
cause unresponsiveness for other users.
I cannot say for sure since I don't have visibility over all
users of the cluster, but unresponsiveness doesn't seem to have
occurred so far. That being said, the fact that it hasn't
occurred yet doesn't mean it won't in the future. So I'm treating
this as a ticking time bomb to be fixed asap.
My questions are the following:
1) Does anyone have experience with large numbers of jobs
submitted in parallel? What are the limits that can be hit? For
example is there some hard limit on how many jobs a SLURM
scheduler can handle before blacking out / slowing down?
2) Is there a way for me to find/measure/ping this resource limit?
3) How can I make sure I don't hit this resource limit?
From what I've observed, parallel submission can improve
submission time by a factor at least 10x. This can make a big
difference in users' workflows.
For that reason I would like to keep the option of launching jobs
sequentially as a last resort.
Thanks in advance.
Regards,
Guillaume.
