Messages in this thread | | | Date | Tue, 17 Oct 2006 19:01:44 -0700 | From | "Siddha, Suresh B" <> | Subject | Re: [RFC] Cpuset: explicit dynamic sched domain control flags |
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On Tue, Oct 17, 2006 at 12:18:23PM -0700, Paul Jackson wrote: > > What happens when the job in the cpuset with no sched domain > > becomes active? In this case, scheduler can't make use of all cpus > > that this cpuset is allowed to use. > > What happens then is that the job manager marks the cpuset of this > newly activated job as being a sched_domain.
With your patch, that will fail because there is already a cpuset defining a sched domain and which overlaps with the one that is becoming active.
So job manager need to set/reset these flags when ever jobs in overlaping cpusets become active/inactive. Is that where you are going with this patch?
What happens when both these jobs/cpusets are active at the same time?
> > And if the job manager doesn't do that, and sets up a situation in > which the scheduler domains don't line up with the active jobs, then > they can't get scheduler load balancing across all the CPUs in those > jobs cpusets. That's exactly what they asked for -- that's exactly > what they got. > > (Actually, is that right? I thought load balancing would still occur > at higher levels in the sched domain/group hierarchy, just not as > often.)
Once the sched domains are partitioned, there is no interaction/scheduling happening between those partitions.
> > It is not the kernels job to make it impossible for user code to do > stupid things. It's the kernels job to offer up various mechanisms, > and let user space code decide what to do when. > > And, anyhow, how does this differ from overloading the cpu_exclusive > flag to define sched domains. One can setup the same thing there, > where a job can't balance across all its CPUs: > > /dev/cpuset/cs1 cpu_exclusive = 1; cpus = 0-7 > /dev/cpuset/cs1/suba cpu_exclusive = 1; cpus = 0-3 > /dev/cpuset/cs1/subb cpu_exclusive = 1; cpus = 4-7 > > (sched_domain_enabled = 0 in all cpusets) > > If you put a task in cpuset "cs1" (not in one of the sub cpusets) > then it can't load balance between CPUs 0-3 and CPUs 4-7 (or can't > load balance as often - depending on how this works.)
hmm... tasks in "cs1" won't properly be balanced between 0-7cpus.. In this case, shouldn't we remove cpus0-3 from "cs1" cpus_allowed?
Current code makes sure that "suba" cpus are removed from "cs1" sched domain but allows the tasks in "cs1" to have "suba" cpus. I don't know much about how job manager interacts with cpusets but this behavior sounds bad to me.
copying Nick to get his thoughts..
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