>>> On Tue, Jan 29, 2008 at 2:04 PM, in message <[EMAIL PROTECTED]>, Paul Jackson <[EMAIL PROTECTED]> wrote: > Gregory wrote: >> IMHO it works well the way it is: The user selects the class for a >> particular task using sched_setscheduler(), and they select the cpuset >> (or inherit it) that defines its execution scope. If that scope has >> balancing enabled, the policy for the member classes is in effect. > > Ok. > > For the various classes of schedulers (sched_class's), it's fine by me > if sched domains are polymorphic, supporting all classes, and it is > left to each task to self-select the scheduling class of its preference. > > For the batch scheduler case, this -must- be imposable from outside > the task, by the batch scheduler that is overseeing the job, and it > must support the batch scheduler being able to disable all the > balancers in selected cpusets (selected sched_domains). > > We have that now. Each of us only knew of part of the solution, > but we managed to arrive at the desired answer even so ... amazing. > > The batch scheduler just has to arrange to get 'sched_load_balance' > turned off in a cpuset and all overlapping cpusets, and then the > CPUS in that cpuset will not belong to -any- sched_domain, and hence > (could you verify I'm right in this detail?) won't be balanced by any > sched_class.
I am a little fuzzy on how this would work, so I cant say for certain. :) But it seems like that is accurate. > > I should update the documentation for sched_load_balance, changing it > from saying that you get realtime by turning off sched_load_balance in > the RT cpuset, to saying that you get realtime by (1) turning off > sched_load_balance in any overlapping cpusets, including all > encompassing parent cpusets, (2) leaving sched_load_balance on in the > RT cpuset itself, and (3) having those realtime tasks each self-select > (elect) the desired SCHED_* using sched_setscheduler(). > > Condition (1) above is a tad difficult to understand, but servicable, > I guess. The combination of (1) and (2) results in a separate > sched_domain just for the CPUs in the RT cpuset. Technically you only need (2). I run my 4-8 core development systems in the single default global cpuset, normally. Customers typically do use multiple sets, but we only use the vanilla balanced variety. > >> (on this topic, note that I do not know if the RT-balancer will >> respect the cpuset concept of "balance-enabled" anyway. That might >> have to be fixed) > > Er eh ... it has no choice. If the user space code has configured a > cpuset with 'sched_load_balance' turned off in that cpuset and all > overlapping cpusets, then there will not even be a sched_domain > covering those CPUs, and hence no balancer, RT or other class, will > even see those CPUs. > > Unless I really don't understand the kernel/sched.c sched_domain code > (a distinct possibility), if some CPU is not in any sched_domain, then > it won't get balanced, RT or otherwise. Heh...I cant quite wrap my head around that, but it sounds like you are correct. The only thing I was really pointing out is that the RT code doesn't necessarily look at sched-domain flags before making balancing decisions. So as long as that is not a requirement, I think we are all set. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
