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SubjectRe: [RFC] [PATCH 0/3] Add group fairness to CFS

* Srivatsa Vaddagiri <vatsa@in.ibm.com> wrote:

> Can you repeat your tests with this patch pls? With the patch applied,
> I am now getting the same split between nice 0 and nice 10 task as
> CFS-v13 provides (90:10 as reported by top )
>
> 5418 guest 20 0 2464 304 236 R 90 0.0 5:41.40 3 hog
> 5419 guest 30 10 2460 304 236 R 10 0.0 0:43.62 3 nice10hog

btw., what are you thoughts about SMP?

it's a natural extension of your current code. I think the best approach
would be to add a level of 'virtual CPU' objects above struct user. (how
to set the attributes of those objects is open - possibly combine it
with cpusets?)

That way the scheduler would first pick a "virtual CPU" to schedule, and
then pick a user from that virtual CPU, and then a task from the user.

To make group accounting scalable, the accounting object attached to the
user struct should/must be per-cpu (per-vcpu) too. That way we'd have a
clean hierarchy like:

CPU #0 => VCPU A [ 40% ] + VCPU B [ 60% ]
CPU #1 => VCPU C [ 30% ] + VCPU D [ 70% ]

VCPU A => USER X [ 10% ] + USER Y [ 90% ]
VCPU B => USER X [ 10% ] + USER Y [ 90% ]
VCPU C => USER X [ 10% ] + USER Y [ 90% ]
VCPU D => USER X [ 10% ] + USER Y [ 90% ]

the scheduler first picks a vcpu, then a user from a vcpu. (the actual
external structure of the hierarchy should be opaque to the scheduler
core, naturally, so that we can use other hierarchies too)

whenever the scheduler does accounting, it knows where in the hierarchy
it is and updates all higher level entries too. This means that the
accounting object for USER X is replicated for each VCPU it participates
in.

SMP balancing is straightforward: it would fundamentally iterate through
the same hierarchy and would attempt to keep all levels balanced - i
abstracted away its iterators already.

Hm?

Ingo
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