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

[Niclas Adlertz]

Yes. SPARC is also included in the results.txt

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. 

Again, sorry for the confusion. 

Kind Regards,
Niclas Adlertz


On 5 sep 2013, at 16:52, Azeem Jiva <azeem.jiva at oracle.com> wrote:

> 
> I agree with Aleksey, the data in raw format is hard to read.  Can you organize the data into a chart or table?  Have you tried a SPARC system?
> 
> 
> --
> Azeem Jiva
> @javawithjiva
> 
> ----- Original Message -----
> From: aleksey.shipilev at oracle.com
> To: niclas.adlertz at oracle.com
> Cc: vladimir.kozlov at oracle.com, hotspot-compiler-dev at openjdk.java.net
> Sent: Thursday, September 5, 2013 7:14:01 AM GMT -08:00 US/Canada Pacific
> Subject: Re: RFR(XS): JDK-8010941: MinJumpTableSize is set to 18, investigate if that's still optimal
> 
> Hi Niclas,
> 
> I have trouble interpreting the results. What are the different numbers after win/loss? Jump table sizes? What is "Not"? Shouldn't "Not" be the same if they are not using the Jump Table? I am very confused.
> 
> -Aleksey
> 
> On 05.09.2013, at 16:41, Niclas Adlertz <niclas.adlertz at oracle.com> wrote:
> 
>> Hi all.
>> 
>> Sorry for the delay.
>> 
>> I've written a JMH test[0] and the results[1] differs from what I previously got. Because of this, I propose the new MinJumpTableSize number to be 10.
>> 
>> WEBREV: http://cr.openjdk.java.net/~adlertz/JDK-8010941/webrev01/
>> 
>> [0]
>> http://cr.openjdk.java.net/~adlertz/JDK-8010941/MyBenchmark.java
>> 
>> [1]
>> http://cr.openjdk.java.net/~adlertz/JDK-8010941/results.txt
>> 
>> Kind Regards,
>> Niclas Adlertz
>> 
>> 
>> On 22 maj 2013, at 00:48, Aleksey Shipilev <aleksey.shipilev at oracle.com> wrote:
>> 
>>> On 05/21/2013 10:17 PM, Vladimir Kozlov wrote:
>>> 
>>>> We usually do about 20000 iterations and run with -Xbatch to make sure
>>>> tested method is compiled before time measurement.
>>> 
>>> Yeah, that works if the benchmark is the single method call. Anything
>>> more complex require more complex warmup.
>>> 
>>>>> Also, I begin to wonder if after the multiply_by_power_of_ten inlining
>>>>> start to affect how far we unroll the loop, since the jump tables are
>>>>> starting to be larger.
>>>> 
>>>> You can avoid it by
>>>> -XX:CompileCommand=dontinline,Test::multiply_by_power_of_ten
>>> 
>>> Or, (chanting) use JMH:
>>> http://hg.openjdk.java.net/code-tools/jmh/file/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_16_CompilerControl.java
>>> 
>>> Or, (chanting again) use JMH, because it does not really use indexed
>>> loops, but rather volatile-predicated loop, so the loop unrolling is
>>> ineffective (double ineffective with the source data re-read from the
>>> fields on every iteration).
>>> 
>>> Before you jump on other platforms, look into the assembly to see if
>>> your benchmark are actually generate the code that makes sense (i.e.
>>> trapped on any of the issues Vladimir and me had speculated here):
>>> https://wiki.openjdk.java.net/display/HotSpot/PrintAssembly
>>> 
>>> -Aleksey.
>>