[slurm-users] Multifactor fair-share with single account

[Ryan Cox]

On 1/4/24 02:41, Kamil Wilczek wrote:
>
>
> W dniu 4.01.2024 o 07:56, Loris Bennett pisze:
>> Hi Kamil,
>>
>> Kamil Wilczek <kmwil at mimuw.edu.pl> writes:
>>
>>> Dear All,
>>>
>>> I have a question regarding the fair-share factor of the multifactor
>>> priority algorithm. My current understanding is that the fair-share
>>> makes sure that different *accounts* have a fair share of the
>>> computational power.
>>>
>>> But what if my organisation structure is flat and I have only one
>>> account where all my user reside. Is fair-share algorithm working
>>> in this situation -- does it take into account users (associations)
>>> from this single account, and tries to assing a fair-factor to each
>>> user? Or each user from this account have the same fair-factor at
>>> each iteration?
>>>
>>> And what if I have, say 3 accounts, but I do not wan't to calculate
>>> fair-share between accounts, but between all associations from all
>>> 3 accounts? In other words, is there a fair-share factor for
>>> users/associations instead of accounts?
>>>
>>> Kind regards
>>
>> We have a similar situation.  We do in fact have an account for each
>> research group and the groups are associated with institutes and
>> departments, but we use FairShare=parent so that all users are given the
>> same number of shares and thus treated equally by the fair-share
>> mechanism.
>>
>
> Hi Loris,
>
> but is the "FairShare=parent" still works for the Fair Tree, which is
> the default algorithm since 19.05? I can find this option only for the
> Classic Fair Share.
>
> And I'm trying to differentiate between users, so that they are not
> treated equally by the algorithm. Heavy users should have a lower
> factor.
>
> I think I could create an account for each user, but is that a common
> practice and not an overkill?
>
> I'm also trying to understand the Fair Tree, because there is a section
> when it says that users can have different factors if their common
> ancestor accounts have different factors. But what if they have only one
> single common ancestor? Would then association/users still be sorted by
> the fair-factor?
>
> Kind regards,

Kamil,

fairshare=parent works for all algorithms, last I knew.  It definitely 
works for Fair Tree.  See https://slurm.schedmd.com/SUG14/fair_tree.pdf 
starting at page 80 for examples of usage.  In page 84, the blue 
associations all have fairshare=parent set, so to fairshare it 
calculates it as if it looks like page 85.  The example on pages 86-91 
actually describe what's going on.

Yes, Fair Tree considers sibling users/accounts even underneath another 
account.  The algorithm is recursive and calculates fairshare amongst 
sibling users/accounts within each account. "sshare -l" will show you 
these calculations under "Level FS" within an account (keeping in mind 
that fairshare=parent will affect what looks like an account to Fair 
Tree).  The presentation I linked to has a lot more details.  
https://slurm.schedmd.com/fair_tree.html is more succinct.

Another way to think about this is that you are only looking at one 
subtree's children at a time.  When one association wins, any of its 
children also win compared to any other associations.  The algorithm 
recurses into that association (if there are children) to then determine 
which of those children win compared to others.  So whether you have a 
flat structure or not, it compares siblings within an account.  If you 
have 100 users directly parented by root (or 100 users underneath 
accounts with fairshare=parent all the way up to root), those 100 users 
will compete for fairshare like you want.

Ryan