RFR(XS): JDK-8010941: MinJumpTableSize is set to 18, investigate if that's still optimal

[Aleksey Shipilev]

On 09/05/2013 06:59 PM, Niclas Adlertz wrote:
> I'll give an example:
> LOSS: At 3:
>   Using JumpTable:
>     Run result "switch_calculation": 166204.989 ±(95%) 52.012 ±(99%) 71.097 ops/msec
>     Run statistics "switch_calculation": min = 166105.218, avg = 166204.989, max = 166602.390, stdev = 111.134
>     Run confidence intervals "switch_calculation": 95% [166152.977, 166257.000], 99% [166133.892, 166276.085]
>   Not:
>     Run result "switch_calculation": 204049.471 ±(95%) 119.901 ±(99%) 163.897 ops/msec
>     Run statistics "switch_calculation": min = 203408.606, avg = 204049.471, max = 204390.380, stdev = 256.193
>     Run confidence intervals "switch_calculation": 95% [203929.570, 204169.372], 99% [203885.574, 204213.368]
> 
> Here, we have tried a switch statement with 3 cases (hence "3") and we lose performance by using a jump table (hence "LOSS"). 
> When we use a jump table ("Using JumpTable") we get the score 166204.989 ops/msec, but when we don't use jump tables ("Not") we can do more ops/msec, 204049.471. 

I get it now, thanks! I was partially confused because the benchmark
only had 16 cases. It is customary for us (perf guys) to create multiple
@GMB methods with different problems sizes, and run them in single JMH
session.

Yes, "10" seems the turn-point for X64; for SPARC, I'd set it to "5".

-Aleksey.