RE: [Sablevm-developer] reflection classes for constant pool and bytecode data

[Andrew P. <apu...@ac...>]

> From: Etienne M. Gagnon <eg...@j-...>
> > John Leuner wrote:
> > I want to point you guys to some papers ( I read some of these last
> > weekend and they gave me lots of food for thought):
> > 
> > http://www-4.ibm.com/software/developer/library/jalapeno/index.html
>
> Mainly:  just keep your mind open and try to push beyond what
> you see other have done!  But, I agree: it is important to know
> about what others have done;-)

I found a related paper ("An Empirical Study of Selective
Optimization"; Matthew Arnold, Michael Hind, and Barbara G.
Ryder; accessable from the link John provided) very interesting.
The result is the conclusion that coarse-grained profiling is
not only sufficient for determining which methods to aggresively
optimize, but is closer to optimal than all other considered
alternatives.

This is good... It means that we can select methods that will
likely benefit from JIT in a simple, low-overhead manner from
within the SableVM interpreter:

  1.  Interrupt normal processing every 10? 100? ms. 

      a.  Determine which method is currently executing.

      b.  If it is native, do nothing further.

      c.  Increment a counter which records how often this
          method was seen executing during profiling. If this
          counter exceeds a minimum value, continue; otherwise
          do nothing further.

      d.  Find (or create) an entry on the JIT's global "to
          do" list for this method (a simple doubly-linked 
          list).

      e.  Look at the previous list entry. If current->count 
          > prev->count; swap prev <-> current. (Only one swap,
          though, not bubblesort!)

      f.  Signal JIT if it is suspended.


  2.  In the JIT thread:

      a.  Remove top entry of "to do" list. If empty, suspend.

      b.  JIT compile.

      c.  goto a


Andy