Proposal for improving performance of TreeMap and others

[cowwoc]

Something very weird is going on. I tried profiling a minimal testcase and
there is a considerable amount of "missing time". I am using a dev build of
Netbeans 6.1 and it says:

MyComparator.compare(Object, Object) 19670ms
\-> MyComparator.compare(Integer, Integer) 10229ms
  \-> Self Time 3001ms
  \-> Integer.compareTo(Integer) 1575ms
\-> Self Time 3788ms

I spot at least three problems:

1) The individual item times do not add up to the total (but they do for
other stack-traces).
2) Comparator.compare() self-time consumes more CPU than Integer.compareTo()
even though it only invokes a method while the latter does actual
computation.
3) Why is extra time consumed moving from MyComparator.compare(Object,
Object) to (Integer, Integer)? It looks like Generics is doing something at
runtime which consumes a large amount of cpu.

Gili


Clemens Eisserer wrote:
> 
> Hi cowwoc,
> 
>> I guess you're right. It is probably as likely that the JIT will optimize
>> away the null check as it is that it will optimize away the
>> NullPointerException check. One exception, though, is when production
>> systems run using -Xverify:none. In such a case, wouldn't my approach run
>> faster?
> I don't think it will optimize the null-check away, however it is so
> cheap that it most likely will not weight at all, compared to all the
> other operations happening there. Its maybe 5 instructions compared to
> thousands or even more.
> -Xverify:none only disables bytecode verification at class-loading
> time and has no influence (as far as I know) on the performance of the
> generated code.
> 
>> I still think that my proposed code is somehow more consistent/cleaner on
>> a
>> design-level but I guess that's just me :)
> I also like it more, its cleaner in my opinion :)
> 
>> As an aside, are there standard benchmarks for testing the impact of this
>> change? I'd love to know whether it actually produces any performance
>> difference in practice.
>>From my experience i would rather guess that you won't notice the
> change, noise will be higher.
> 
> lg Clemens
> 
> 

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