[slurm-users] slurm power save question

[Brian Andrus]

Sorry for the late reply.

For my site, I used the optional ":" separator to ensure at least 4 
nodes were up. Eg: nid[10-20]:4
This means at least 4 nodes.. those nodes do not have to be the same 4 
at any time, so if one is down that used to be idle, but 4 are up, that 
1 will not be brought back up. I don't see this setting having much of 
anything to do with bringing nodes up at all with the exception of when 
you first start slurmctld and the settings are not met. Once there are 
jobs running on any of the listed nodes, they count toward the number. 
That is my experience with the small numbers I used. YMMV.

I have also explicitly stated nodes without the separator, which does 
work. I do that when I am trying to look at a node that is idle without 
a job on it. That stops slurm from shutting it down while I am looking 
at it.

Although, I do agree, the functionality of being able to have "keep at 
least X nodes up and idle" would be nice, that is not how I see this 
documented or working.

Brian Andrus

On 11/23/2023 5:12 AM, Davide DelVento wrote:
> Thanks for confirming, Brian. That was my understanding as well. Do 
> you have it working that way on a machine you have access to?  If so, 
> I'd be interested to see the config file, because that's not the 
> behavior I am experiencing in my tests.
> In fact, in my tests Slurm will not bring down those "X nodes" but 
> will not bring them up either, *unless* there is a job targeted to 
> those. I may have something misconfigured, and I'd love to fix that.
>
> Thanks!
>
> On Wed, Nov 22, 2023 at 5:46 PM Brian Andrus <toomuchit at gmail.com> wrote:
>
>     As I understand it, that setting means "Always have at least X
>     nodes up", which includes running jobs. So it stops any wait time
>     for the first X jobs being submitted, but any jobs after that will
>     need to wait for the power_up sequence.
>
>     Brian Andrus
>
>     On 11/22/2023 6:58 AM, Davide DelVento wrote:
>>     I've started playing with powersave and have a question about
>>     SuspendExcNodes. The documentation at
>>     https://slurm.schedmd.com/power_save.html says
>>
>>     For example |nid[10-20]:4| will prevent 4 usable nodes (i.e IDLE
>>     and not DOWN, DRAINING or already powered down) in the set
>>     |nid[10-20]| from being powered down.
>>
>>     I initially interpreted that as "Slurm will try to keep 4 nodes
>>     idle on as much as possible", which would have reduced the wait
>>     time for new jobs targeting those nodes. Instead, it appears to
>>     mean "Slurm will not shut off the last 4 nodes which are idle in
>>     that partition, however it will not turn on nodes which it shut
>>     off earlier unless jobs are scheduled on them"
>>
>>     Most notably if the 4 idle nodes will be allocated to other jobs
>>     (and so they are no idle anymore) slurm does not turn on any
>>     nodes which have been shut off earlier, so it's possible (and
>>     depending on workloads perhaps even common) to have no idle nodes
>>     on regardless of the SuspendExcNode settings.
>>
>>     Is that how it works, or do I have anything else in my setting
>>     which is causing this unexpected-to-me behavior? I think I can
>>     live with it, but IMHO it would have been better if slurm
>>     attempted to turn on nodes preemptively trying to match the
>>     requested SuspendExcNodes, rather than waiting for job submissions.
>>
>>     Thanks and Happy Thanksgiving to people in the USA
>
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