Peter Williams <[email protected]> wrote:
>
> Andrew Morton wrote:
> > "Siddha, Suresh B" <[email protected]> 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.
OK.
> 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.
Sure, we can leave things like that until later.
> > Has sufficient testing been done for us to
> > know this?
I should have said "testing for regressions". We know that smpnice
improves some things. My concern is that it doesn't cause any non-silly
workloads to worsen. Once we're at that stage I think we're ready to go.
IOW: at this stage we should concentrate upon not taking any workloads
backwards, rather than upon taking even more workloads even more forwards.
That can come later.
> 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.
Sure. A mortal doesn't have the hardware and isn't set up to test certain
high-value workloads...
> As load balancing is inherently probabilistic I don't think that we
> should hold out for "perfect".
Sure. "same or better" is the aim here.
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