Messages in this thread | | | Date | Wed, 8 Jan 2014 13:45:16 +0000 | From | Morten Rasmussen <> | Subject | Re: [RFC] sched: CPU topology try |
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On Wed, Jan 08, 2014 at 01:32:57PM +0000, Peter Zijlstra wrote: > On Wed, Jan 08, 2014 at 01:27:39PM +0000, Morten Rasmussen wrote: > > On Wed, Jan 08, 2014 at 12:45:34PM +0000, Peter Zijlstra wrote: > > > On Wed, Jan 08, 2014 at 12:35:34PM +0000, Morten Rasmussen wrote: > > > > > Currently we detect overload by sg.nr_running >= sg.capacity, which can > > > > > be very misleading because while a cpu might have a task running 'now' > > > > > it might be 99% idle. > > > > > > > > > > At which point I argued we should change the capacity thing anyhow. Ever > > > > > since the runnable_avg patch set I've been arguing to change that into > > > > > an actual utilization test. > > > > > > > > > > So I think that if we measure overload by something like >95% utilization > > > > > on the entire group the load scaling again makes perfect sense. > > > > > > > > I agree that it make more sense to change the overload test to be based > > > > on some tracked load. How about the non-overloaded case? Load balancing > > > > would have to be based on unweighted task loads in that case? > > > > > > Yeah, until we're overloaded our goal is to minimize idle time. > > > > I would say, make the most of the available cpu cycles. Minimizing idle > > time is not always the right thing to do when considering power > > awareness. > > > > If we know the actual load of the tasks, we may be able to consolidate > > I think we must start to be careful with the word load, I think you > meant to say utilization.
Indeed, I meant utilization.
> > > them on fewer cpus and save power by idling cpus. In that case the idle > > time (total) is unchanged (unless the P-state is changed). Somewhat > > similar to the video use-case running on 1, 2, and 4 cpu that I reposted > > yesterday. > > But fair enough.. Its idle time when you consider CPUs to always run at > max frequency, but clearly I must stop thinking about CPUs like that :-)
Yes, it opens a whole new world of problems to be solved :-)
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