On Mon, Nov 19, 2012 at 11:37:01PM -0800, David Rientjes wrote:

On Tue, 20 Nov 2012, Ingo Molnar wrote:

quoted

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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