Branch Prediction?

[Mikael Gerdin]

On 2014-11-20 16:04, Andrew Haley wrote:
> On 11/20/2014 02:28 PM, Paul Hohensee wrote:
>> If it were me (and it's not :) ), I'd want to see some generated code
>> examples that would benefit.  Perhaps quantify the benefit by getting a
>> libjvm profile, look at the code for the top 10 or 20 methods, reorganize
>> it via a proof-of-concept implementation and measure the result.  I'd also
>> take into consideration that future hardware improvements (e.g., larger
>> icache line size) might negate any current improvement, so it'd have to be
>> a 'big' benefit.  Again if it were me (and it's not :) ), it would take
>> maybe a per-instance 10% improvement before I'd accept the intellectual
>> overhead cost of a permanent implementation. I worry a lot about long term
>> source code maintainability, hence I have a sort of automatic skepticism
>> about features than complicate it. :)
>
> I agree, but:
>
> The problem with the "benchamrk and see" approach is that a fast
> system is made up of many very small optimizations, each one of which
> may be lost in the noise.

+1

I, personally, would be fine with adding these kinds of hints to the hot 
paths of the scavenging collectors, for example.
But someone needs to do the actual performance measurements to show that 
it at least gives something.

/Mikael

>
> Andrew.
>