Messages in this thread | | | From | Con Kolivas <> | Subject | Re: [rfc][patch] sched: remove smpnice | Date | Wed, 8 Feb 2006 10:11:09 +1100 |
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On Wed, 8 Feb 2006 09:15 am, Andrew Morton wrote: > Con Kolivas <kernel@kolivas.org> 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?
No benchmark improved but 'nice' handling moved from completely not working on SMP to having quite effective cpu resource modification according to nice. nice 19 vs nice 0 has 5% of the cpu on UP. On SMP machines without smp nice if you have more tasks than cpus (the 5 tasks on 4 cpu example) you often get nice 19 tasks getting more cpu resources than nice 0 tasks; a nice 19 task would get 100% of one cpu and two nice 0 tasks would get 50% of a cpu. With smp nice the nice 19 task received between 5-30% of one cpu depending on their sleep/wake pattern.
> Because if we have one workload which slowed and and none which sped up, > it's a pretty easy decision..
The resource allocation fairness was improved with smp nice but no benchmark directly sped up per se.
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