Messages in this thread |  | | Date | Mon, 10 Oct 2016 14:04:25 +0200 | From | Peter Zijlstra <> | Subject | Re: About group scheduling for SCHED_DEADLINE |
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On Mon, Oct 10, 2016 at 12:15:58PM +0200, Peter Zijlstra wrote: > Right, so the problem we have is unspecified SCHED_FIFO on SMP and > historical behaviour. > > As you know we've extended FIFO to SMP by G-FIFO (run the m highest prio > tasks on m CPUs). But along with that, we allow arbitrary affinity masks > for RR/FIFO tasks. > > (Note that RR is broken in the G-FIFO model, but that's a different > discussion for a different day). > > Now, the proposed model has identical CBS parameters for every (v)cpu of > the cgroup. This means that a cgroup must be overprovisioned in the > general case where nr_tasks < nr_cpus (and worse, the parameters must > match the max task). > > This leads to vast amounts of wasted resources. > > The alternative is different but fixed parameters per cpu, but that is > somewhat unwieldy in that it increases the configuration burden. But you > can indeed minimize the wasted resources and deal with the affinity > problem (AFAICT). >
Hurm, so I think both proposals above rely on deadline servers with single CPU affinity, something which we currently do not support at all, and is something that should be defined/fixed first I think.
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