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From "Aleksey Shipilev" <aleksey.shipi...@gmail.com>
Subject Re: [general][performance] Stefan Krause's Harmony performance evaluation
Date Fri, 04 Jul 2008 08:35:17 GMT
Hi Gregory, all,

The performance is important for JRE too.

BTW, I had profiled spectralnorm benchmark and see following problems:

1. Bad instruction selection for integer divide:

int a;
int b = a / 2;

generates into:

mov eax, a
mov ebx, 2
idiv eax, ebx

but it's better to

mov eax, a
shl eax, 1

Manual change in Java code brings +60% to spectralnorm performance
(execution time downs from 10secs to 6secs). There should be better
instruction selection for divide operation. Would someone take it? If
not, I would try to produce the patch for Jitrino this weekend.

2. Recompilation events propagation

Consider the following call chain:
main() --[n times]--> A() --[m times]--> B()

Now consider, m >> n, then B() should be inlined. But such the
inlining will be done during the recompilation of method A(), which
waits for n to rise up (that's true for current server.emconf with
edge profiler enabled). On first glance, one of the solutions will be
propagation of such recompilation requests up the call chain. Any
ideas here are welcome.


On Fri, Jul 4, 2008 at 1:04 AM, Gregory Shimansky <gshimansky@apache.org> wrote:
> On 4 июля 2008 Aleksey Shipilev wrote:
>> Stefan Krause publishes another review on Java vs. C performance here:
>> http://www.stefankrause.net/wp/?p=9#comments
>> It seems like Harmony has "a long way to go" in performance :)
>> I'm gonna look on some of these tests in near term.
> It is interesting to see that IBM is often quite close to Harmony in
> performance. In fact Harmony acts quite well in its current state. I think
> though that performance for Java is always a 2nd priority after stability.
> Look at IBM, its Java is targeted at servers where stability is what is
> important.
> Looking at the occasional test failures on the alerts mail list it seems like
> stability is the number one focus for improvement and it is a by far harder
> to move in that direction.
> --
> Gregory
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