Re: [rfc][patch] sched: remove smpnice

[Andrew Morton]

Con Kolivas <kernel@xxxxxxxxxxx> wrote:
>
> On Wednesday 08 February 2006 01:28, Nick Piggin wrote:
> > I'd like to get some comments on removing smpnice for 2.6.16. I don't
> > think the code is quite ready, which is why I asked for Peter's additions
> > to also be merged before I acked it (although it turned out that it still
> > isn't quite ready with his additions either).
> >
> > Basically I have had similar observations to Suresh in that it does not
> > play nicely with the rest of the balancing infrastructure (and raised
> > similar concerns in my review).
> >
> > The samples (group of 4) I got for "maximum recorded imbalance" on a 2x2
> >
> > SMP+HT Xeon are as follows:
> >            | Following boot | hackbench 20        | hackbench 40
> >
> > -----------+----------------+---------------------+---------------------
> > 2.6.16-rc2 | 30,37,100,112  | 5600,5530,6020,6090 | 6390,7090,8760,8470
> > +nosmpnice |  3, 2,  4,  2  |   28, 150, 294, 132 |  348, 348, 294, 347
> >
> > Hackbench raw performance is down around 15% with smpnice (but that in
> > itself isn't a huge deal because it is just a benchmark). However, the
> > samples show that the imbalance passed into move_tasks is increased by
> > about a factor of 10-30. I think this would also go some way to
> > explaining latency blips turning up in the balancing code (though I
> > haven't actually measured that).
> >
> > We'll probably have to revert this in the SUSE kernel.
> >
> > The other option for 2.6.16 would be to fast track Peter's stuff, which
> > I could put some time into... but that seems a bit risky at this stage
> > of the game.
> >
> > I'd like to hear any other suggestions though. Patch included to aid
> > discussion at this stage, rather than to encourage any rash decisions.
> 
> I see the demonstrable imbalance but I was wondering if there is there a real 
> world benchmark that is currently affected?
> 

Well was any real-world workload (or benchmark) improved by the smpnice
change?

Because if we have one workload which slowed and and none which sped up,
it's a pretty easy decision..
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