Implementing a Smalltalk debugger with JSR292

[Mark Roos]

Hi Helmut,

The problem I saw before was due to enabling all of the capabilities of 
jvmti.  Since then I
backed off to only the capabilities I use.  With this change my original 
benchmarks do not show any
slowdown.   This was one of the reasons I chose to try this approach to 
stepping rather than use jvmti.
There is still the question of does adding the debug test in front of 
every call add much time.   This is 
on my list of things to find out. 

As to how Rtalk( mine)  compares with Smalltalk.  Well that really depends 
on the benchmark chosen.
The big issue I see is my decision to use boxed integers for all uses vs 
the use of primitive integers
by both the jvm and Smalltalk.  For my Hanoi benchmark ( lots of ints ) I 
run about 10x slower than
Smalltalk ( vs java being 50% faster than Smalltalk).  But if I code in 
java as Rtalk does by using boxed integers hidden
within other objects the java time becomes 5x slower than Smalltalk.  So I 
think some looking at the use
of integers would be the big benchmark gain.  Some easy things would be an 
integer cache (as
garbage is a big part of the time lost) and having the compiler use 
primitives for hidden loop counters
and iterators.

Having said that, for complex applications which spend lots of time in 
primitives ( string handling and
float vectors) Rtalk is actually faster than Smalltalk.  My application is 
a DSL compiler with a runtime
which spend most of its time handling byteArrays and floatVectors  so I am 
expecting to see the jvm
version being faster.

An added advantage I see is the ability to use java as the language to 
write user primitives in.  This would
make implementing local speed up methods quite easy

I will let you know as it progresses

regards
mark

mlvm-dev-bounces at openjdk.java.net wrote on 11/27/2011 01:07:50 AM:

> From: Helmut Eller <eller.helmut at gmail.com>
> To: mlvm-dev at openjdk.java.net
> Date: 11/27/2011 01:24 AM
> Subject: Re: Implementing a Smalltalk debugger with JSR292
> Sent by: mlvm-dev-bounces at openjdk.java.net
> 
> * Mark Roos [2011-11-27 06:16] writes:
> 
> > The approach we took has two facets, we ( mainly oscar ) coded a C++
> > jvmti agent with a JNI interface which allowed us to call some JVMTI
> > apis from within the jvm being debugged and we added some logic to the
> > callsite to handle the stepping.
> 
> What's the cost of this approach?  In a previous post you said that
> enabling the debug agent degraded performance of the JVM considerably.
> If the debugger enabled in "production mode"?  How does the efficiency
> of your system compare to native Smalltalks?
> 
> Helmut
> 
> _______________________________________________
> mlvm-dev mailing list
> mlvm-dev at openjdk.java.net
> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.openjdk.java.net/pipermail/mlvm-dev/attachments/20111127/52442e16/attachment.html