On Thu, Nov 30, 2017 at 2:52 PM, Benjamin Bannier < benjamin.bann...@mesosphere.io> wrote:
> Hi Ben, > > and thank you for answering. > > > > For frameworks in the same role on the other hand we choose to > normalize > > > with the allocated resources > > > > Within a role, the framework's share is evaluated using the *role*'s > total > > allocation as a denominator. Were you referring to the role's total > > allocation when you said "allocated resources"? > > Yes. > > > I believe this was just to reflect the "total pool" we're sharing within. > > For roles, we're sharing the total cluster as a pool. For frameworks > within > > a role, we're sharing the role's total allocation as a pool amongst the > > frameworks. Make sense? > > Looking at the allocation loop, I see that while a role sorter uses the > actual cluster resources when generating a sorting, we only seem to > update the total in the picked framework sorter with an `add` at the end > of the allocation loop, so at the very least the "total pool" of > resources in a single role seems to lag. Should this update be moved to > the top of the loop? > Yes, the role's allocation pool should be adjusted before the framework sorting. > > > The sort ordering should be the same no matter which denominator you > > choose, since everyone gets the same denominator. i.e. 1,2,3 are ordered > > the same whether you're evaluating their share as 1/10,2/10,3/10 or > > 1/100,2/100,3/100, etc. > > This seems to be only true if we have just a single resource kind. For > multiple resource kinds we are not just dealing with a single scale > factor, but will also end up comparing single-resource scales against > each other in DRF. > > Here's a brief example of a cluster with two frameworks where we end up > with different DRF weights `f` depending on whether the frameworks are in > the same role or not. > > - Setup: > * cluster total: cpus:40; mem:100; disk:1000 > * cluster used: cpus:30; mem: 2; disk: 5 > > * framework 'a': used=cpus:20; mem:1; disk:1 > * framework 'b': used=cpus:10; mem:1; disk:4 > > - both frameworks in separate roles > * framework 'a', role 'A'; role shares: cpus:2/4; mem:1/100; > disk:1/1000; f=2/4 > * framework 'b', role 'B'; role shares: cpus:1/4; mem:1/100; > disk:2/1000; f=1/4 > > - both frameworks in same role: > * framework 'a': framework shares: cpus:2/3; mem:1/2; disk:1/4; f=1/2 > * framework 'b': framework shares: cpus:1/3; mem:1/2; disk:4/5; f=4/5 > > If each framework is in its own role we would allocate the next resource > to 'b'; if the frameworks are in the same role we would allocate to 'a' > instead. This is what I meant with > > > It appears to me that by normalizing with the used resources inside a > role > > we somehow bias allocations inside a role against frameworks with > “unusual” > > usage vectors (relative to other frameworks in the same role). > > In this example we would penalize 'b' for having a usage vector very > different from 'a' (here: along the `disk` axis). > Ah yes, thanks for clarifying. The role's allocation pool that the frameworks in that role are sharing may have a different ratio of resources compared to the total cluster. > > > Benjamin >
