Kernel 2.6 on MPC8xx performance trouble...

[Wolfgang Denk]

In message <200510281257.22650.david.jander at protonic.nl> you wrote:
>
> > What is 'a' and 'b'? The only other explanation I can see is that your
> > "Do something" is more memory heavy than you think - array calculations?
> > (Cache problems should probably give a worse result, but you could check
> > that those config registers are the same).
> 
> They are just integers with fixed start values. These are in the loop, so it's 
> not an empty loop and hopefully the compiler won't out-optimize it so easily 
> (that is of course without specifying any optimization flags). Please don't 
> tell me it's a lousy benchmark, because I already know that! Be it as lousy 
> as it is, I shouldn't get _those_ results IMHO.

Indeed, you should not get such results.  If  you  compare  with  the
lmbench  results  of  our 2.4/2.6 comparison, you will notice that we
did NOT see such behaviour. There was a  perfromnce  degradation  for
pure  integer tests, due to increased system overhead, but far from a
factor of 2.
See http://www.denx.de/wiki/pub/Know/Linux24vs26/lmbench_results

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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