Srivatsa Vaddagiri wrote:
Good example :) USER2's single task will have to share its CPU with
USER1's 50 tasks (unless we modify the smpnice load balancer to
disregard cpu affinity that is - which I would not prefer to do).
I don't think that ignoring cpu affinity is an option. Setting the cpu
affinity of tasks is a deliberate policy action on the part of the
system administrator and has to be honoured. Load balancing has to do
the best it can in these circumstances which may mean sub optimal
distribution of the load BUT it is result of a deliberate policy
decision by the system administrator.
Ingo/Peter, any thoughts here? CFS and smpnice probably is "broken"
with respect to such example as above albeit for nice-based tasks.
See above. I think that faced with cpu affinity use by the system
administrator that smpnice will tend towards a task to cpu allocation
that is (close to) the best that can be achieved without violating the
cpu affinity assignments. (It may take a little longer than normal but
it should get there eventually.)
You have to assume that the system administrator knows what (s)he's
doing and is willing to accept the impact of their policy decision on
the overall system performance.
Having said that, if it was deemed necessary you could probably increase
the speed at which the load balancer converged on a good result in the
face of cpu affinity by keeping a "pinned weighted load" value for each
run queue and using that to modify find_busiest_group() and
find_busiest_queue() to be a bit smarter. But I'm not sure that it
would be worth the added complexity.
Peter
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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