Messages in this thread | | | Date | Fri, 21 Apr 2006 10:28:02 +1000 | From | Peter Williams <> | Subject | Re: [patch] smpnice: don't consider sched groups which are lightly loaded for balancing |
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Andrew Morton wrote: > "Siddha, Suresh B" <suresh.b.siddha@intel.com> wrote: >> updated patch appended. thanks. > > Where are we up to with smpnice now? Are there still any known > regressions/problems/bugs/etc?
One more change to move_tasks() is required to address an issue raised by Suresh w.r.t. the possibility unnecessary movement of the highest priority task from the busiest queue (possible because of the active/expired array mechanism). I hope to forward a patch for this later today.
After that the only thing I would like to do at this stage is modify try_to_wake_up() so that it tries harder to distribute high priority tasks across the CPUs. I wouldn't classify this as absolutely necessary as it's really just a measure that attempts to reduce latency for high priority tasks as it should get them onto a CPU more quickly than just sticking them anywhere and waiting for load balancing to kick in if they've been put on a CPU with a higher priority task already running. Also it's only really necessary when there a lot of high priority tasks running. So this isn't urgent and probably needs to be coordinated with Ingo's RT load balancing stuff anyway.
> Has sufficient testing been done for us to > know this?
I run smpnice kernels on all of my SMP machines all of the time. But I don't have anything with more than 2 CPUs so I've been relying on their presence in -mm to get wider testing on larger machines.
I think that once this patch and the move_tasks() one that I'll forward later today are incorporated we should have something that (although not perfect) works pretty well. Neither of these changes should cause a behavioural change in the case where all tasks are nice==0.
As load balancing is inherently probabilistic I don't think that we should hold out for "perfect".
Peter -- Peter Williams pwil3058@bigpond.net.au
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