[slurm-users] scontrol reboot does not allow new jobs to be scheduled if nextstate=RESUME is set

[Tim Schneider]

Hi,

from my understanding, if I run "scontrol reboot <node>", the node
should continue to operate as usual and reboots once it is idle. When
adding the ASAP flag (scontrol reboot ASAP <node>), the node should go
into drain state and not accept any more jobs.

Now my issue is that when I run "scontrol reboot ASAP nextstate=RESUME
<node>", the node goes in "mix@" state (not drain), but no new jobs get
scheduled until the node reboots. Essentially I get draining behavior,
even though the node's state is not "drain". Note that this behavior is
caused by "nextstate=RESUME"; if I leave that away, jobs get scheduled
as expected. Does anyone have an idea why that could be?

I am running slurm 22.05.9.

Steps to reproduce:

# To prevent node from rebooting immediately
sbatch -t 1:00:00 -c 1 --mem-per-cpu 1G -w <node> ./long_running_script.sh

# Request reboot
scontrol reboot nextstate=RESUME <node>

# Run interactive command, which does not start until "scontrol
cancel_reboot <node>" is executed in another shell
srun -t 1:00:00 -c 1 --mem-per-cpu 1G -w <node> --pty bash


Thanks a lot in advance!

Best,

Tim

[Christopher Samuel]

On 10/24/23 12:39, Tim Schneider wrote:

> Now my issue is that when I run "scontrol reboot ASAP nextstate=RESUME
> <node>", the node goes in "mix@" state (not drain), but no new jobs get
> scheduled until the node reboots. Essentially I get draining behavior,
> even though the node's state is not "drain". Note that this behavior is
> caused by "nextstate=RESUME"; if I leave that away, jobs get scheduled
> as expected. Does anyone have an idea why that could be?

The intent of the "ASAP` flag for "scontrol reboot" is to not let any
more jobs onto a node until it has rebooted.

IIRC that was from work we sponsored, the idea being that (for how our
nodes are managed) we would build new images with the latest software
stack, test them on a separate test system and then once happy bring
them over to the production system and do an "scontrol reboot ASAP
nextstate=resume reason=... $NODES" to ensure that from that point
onwards no new jobs would start in the old software configuration, only
the new one.

Also slurmctld would know that these nodes are due to come back in
"ResumeTimeout" seconds after the reboot is issued and so could plan for
them as part of scheduling large jobs, rather than thinking there was no
way it could do so and letting lots of smaller jobs get in the way.

Hope that helps!

All the best,
Chris
--
Chris Samuel : http://www.csamuel.org/ : Berkeley, CA, USA

[Tim Schneider]

Hi Chris,

thanks a lot for your response.

I just realized that I made a mistake in my post. In the section you
cite, the command is supposed to be "scontrol reboot nextstate=RESUME"
(without ASAP).

So to clarify: my problem is that if I type "scontrol reboot
nextstate=RESUME" no new jobs get scheduled anymore until the reboot. On
the other hand, if I type "scontrol reboot", jobs continue to get
scheduled, which is what I want. I just don't understand, why setting
nextstate results in the nodes not accepting jobs anymore.

My usecase is similar to the one you describe. We use the ASAP option
when we install a new image to ensure that from the point of the
reinstallation onwards, all jobs end up on nodes with the new
configuration only. However, in some cases when we do only minor changes
to the image configuration, we prefer to cause as little disruption as
possible and just reinstall the nodes whenever they are idle. Here,
being able to set nextstate=RESUME is useful, since we usually want the
nodes to resume after reinstallation, no matter what their previous
state was.

Hope that clears it up and sorry for the confusion!

Best,

tim

On 25.10.23 02:10, Christopher Samuel wrote:
> On 10/24/23 12:39, Tim Schneider wrote:
>

>> Now my issue is that when I run "scontrol reboot ASAP nextstate=RESUME
>> <node>", the node goes in "mix@" state (not drain), but no new jobs get
>> scheduled until the node reboots. Essentially I get draining behavior,
>> even though the node's state is not "drain". Note that this behavior is
>> caused by "nextstate=RESUME"; if I leave that away, jobs get scheduled
>> as expected. Does anyone have an idea why that could be?

[Ole Holm Nielsen]

Hi Tim,

I think the scontrol manual page explains the "scontrol reboot" function
fairly well:

> reboot [ASAP] [nextstate={RESUME|DOWN}] [reason=<reason>]
> {ALL|<NodeList>}
> Reboot the nodes in the system when they become idle using the
> RebootProgram as configured in Slurm's slurm.conf file. Each
> node will have the "REBOOT" flag added to its node state. After
> a node reboots and the slurmd daemon starts up again, the
> HealthCheckProgram will run once. Then, the slurmd daemon will
> register itself with the slurmctld daemon and the "REBOOT" flag
> will be cleared. The node's "DRAIN" state flag will be cleared
> if the reboot was "ASAP", nextstate=resume or down. The "ASAP"
> option adds the "DRAIN" flag to each node's state, preventing
> additional jobs from running on the node so it can be rebooted
> and returned to service "As Soon As Possible" (i.e. ASAP).

It seems to be implicitly understood that if nextstate is specified, this
implies setting the "DRAIN" state flag:

> The node's "DRAIN" state flag will be cleared if the reboot was "ASAP", nextstate=resume or down.

You can verify the node's DRAIN flag with "scontrol show node <nodename>".

IMHO, if you want nodes to continue accepting new jobs, then nextstate is
irrelevant.

We always use "reboot ASAP" because our cluster is usually so busy that
nodes never become idle if left to themselves :-)

FYI: We regularly make package updates and firmware updates using the
"scontrol reboot asap" method which is explained in this script:
https://github.com/OleHolmNielsen/Slurm_tools/blob/master/nodes/update.sh

Best regards,
Ole,
Ole

[Tim Schneider]

Hi Ole,

thanks for your reply.

The curious thing is that when I run "scontrol reboot nextstate=RESUME
<node>", the drain flag of that node is not set (sinfo shows mix@ and
"scontrol show node <node>" shows no DRAIN in State, just
MIXED+REBOOT_REQUESTED), yet no jobs are scheduled on that node until
reboot. If I specifically request that node for a job with "-w <node>",
I get "Nodes required for job are DOWN, DRAINED or reserved for jobs in
higher priority partitions".

Not using nextstate=RESUME is inconvenient for me as sometimes we have
parts of our cluster drained and I would like to run a single command
that reboots all non-drained nodes once they become idle and all drained
nodes immediately, resuming them once they are done reinstalling.

Best,

Tim