On Mon, Nov 19, 2012 at 11:37:01PM -0800, David Rientjes wrote:
> On Tue, 20 Nov 2012, Ingo Molnar wrote:
>
> > No doubt numa/core should not regress with THP off or on and
> > I'll fix that.
> >
> > As a background, here's how SPECjbb gets slower on mainline
> > (v3.7-rc6) if you boot Mel's kernel config and turn THP forcibly
> > off:
> >
> > (avg: 502395 ops/sec)
> > (avg: 505902 ops/sec)
> > (avg: 509271 ops/sec)
> >
> > # echo never > /sys/kernel/mm/transparent_hugepage/enabled
> >
> > (avg: 376989 ops/sec)
> > (avg: 379463 ops/sec)
> > (avg: 378131 ops/sec)
> >
> > A ~30% slowdown.
> >
> > [ How do I know? I asked for Mel's kernel config days ago and
> > actually booted Mel's very config in the past few days,
> > spending hours on testing it on 4 separate NUMA systems,
> > trying to find Mel's regression. In the past Mel was a
> > reliable tester so I blindly trusted his results. Was that
> > some weird sort of denial on my part? :-) ]
> >
>
> I confirm that numa/core regresses significantly more without thp than the
> 6.3% regression I reported with thp in terms of throughput on the same
> system. numa/core at 01aa90068b12 ("sched: Use the best-buddy 'ideal cpu'
> in balancing decisions") had 99389.49 SPECjbb2005 bops whereas
> ec05a2311c35 ("Merge branch 'sched/urgent' into sched/core") had 122246.90
> SPECjbb2005 bops, a 23.0% regression.
>
I also see different regressions and gains depending on the number of
warehouses. For low number of warehouses without THP the regression was
severe but flat for higher number of warehouses. I explained in another
mail that specjbb reports based on peak figures and regressions outside
the peak can be missed as a result so we should watch out for that.
--
Mel Gorman
SUSE Labs
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