[OpenBIOS] PATCH: Implement Forth source debugger for OpenBIOS

[Mark Cave-Ayland]

Mark Cave-Ayland wrote:

> Indeed. I had a similar inspiration earlier this evening, with the only 
> problem being how to switch code into next() without causing a 
> performance hit. However, I think I've just worked out a cute little 
> hack that would solve this. I'm at a conference over the next few days, 
> so it might not be until next week that I get a chance re-work the patch 
> and resubmit.

Okay, so I've come across an interesting problem with regard to 
reworking this. Attached is a patch that demonstrates some very alarming 
behaviour, at least here on x86_64 gcc 4.3.2. What happens is that just 
by adding a single function pointer to kernel/internal.c, the runtime 
for my fibonacci benchmark goes up by 40%!

With the attached patch for OpenBIOS SVN, I get the following runtime 
for the Fibonacci benchmark:


build at zeno:~/src/openbios/openbios-devel$ time echo "28 fib-rec u. bye" 
| ./obj-x86/openbios-unix ./obj-x86/openbios-x86.dict
Welcome to OpenBIOS v1.0 built on Nov 9 2009 17:17
   Type 'help' for detailed information

[unix] Booting default not supported.

0 > 28 fib-rec u. bye 6197ecb
Farewell!

  ok

real    0m52.564s
user    0m52.027s
sys     0m0.012s


If the line "void (*debughook) (void);" is then commented out from 
kernel/internal.c then the runtime looks like below (which is roughly 
the same as running the fib-rec benchmark on plain OpenBIOS SVN):


build at zeno:~/src/openbios/openbios-devel$ time echo "28 fib-rec u. bye" 
| ./obj-x86/openbios-unix ./obj-x86/openbios-x86.dict
Welcome to OpenBIOS v1.0 built on Nov 9 2009 17:12
   Type 'help' for detailed information

[unix] Booting default not supported.

0 > 28 fib-rec u. bye 6197ecb
Farewell!

  ok

real    0m37.946s
user    0m37.178s
sys     0m0.020s


So in other words, simply defining a pointer variable (which hasn't even 
been used anywhere in the code yet) is increasing the runtime by 40%?! 
Can anyone shed any light on this behaviour? It just doesn't seem to 
make any sense to me.


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
http://www.siriusit.co.uk
t: +44 870 608 0063

Sirius Labs: http://www.siriusit.co.uk/labs
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