Psyco-friendly patch #2.

A very very small statistic-collecting patch.


pystate.h: added a field at the end of the
PyThreadStruct:

    int tick_counter;

ceval.c: eval_frame():

    tstate->tick_counter is incremented whenever the
    check_interval ticker reaches zero.

The purpose is to give a useful measure of the number
of interpreted
bytecode instructions in a given thread.  This
extremely lightweight
statistic collector can be of interest to profilers
(like psyco.jit()).

We can safely guess that a single integer increment
every 100
interpreted bytecode instructions will go entierely
unnoticed
in any performance measure. [This is true for
pystone.py.]

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I see no harm in this.

Are you sure it's actually going to be useful, though?

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It is the only way I could work out so far that can
"predict" how much a function will be accelerated when run
under Psyco.  This is a very precious indication for an
automatic Psyco-binder.  The following table shows the
results with the various test functions of the
distribution's "test.py" file:

(fn name)     (speed-up)  (bytecode insns per second)
f1              106.00         
2310545                        
f4              11.33          
2819100                        
f5              12.08          
2992445                        
f6              1.35           
412022                         
f7              2.24           
1331353                        
f7bis           10.29          
1632296                        

The third column is '(tick_counter * check_interval) /
execution_time'.  The correlation between the two columns is
admittedly not perfect, but still we can see that it was not
worthy to try and accelerate f6 because it didn't spend a
lot of time actually interpreting bytecodes.

Note that similar information could be obtained by setting a
line-tracing hook, counting not instructions but lines
(which is less precise but still a good approximation). 
However, line tracing is *much* too slow for anything but
debugging usage.

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I'd like to get this into 2.2.2. MWH, can you check it in?

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Done in

Include/pystate.h revision 2.18.16.1
Python/ceval.c revision 2.301.4.7

Armin, I don't know how you generated this patch, but it
would have been easier to apply if it had been rooted in the
"src" directory, like e.g.:

$ cvs diff Include/pystate.h Python/ceval.c > ~/diff

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Uploaded the 2.3 patch (this one cleanly generated -- for the 
other one I just cat'ed two patches in one).

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Attached an updated diff for 2.3.  This one doesn't have
Windows line endings and includes the initialization of
tick_counter to 0 that was added by Guido in the latest
2.2.2.  (I thought it was unnecessary to initialize it to
anything because profilers would only be interested in
differences.)

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I got lazy and checked in all the psyco patches at once:

Include/pystate.h revision 2.21
Modules/pyexpat.c revision 2.76
Python/ceval.c revision 2.340
Python/pystate.c revision 2.22