[OpenBIOS] compiler speed

Segher Boessenkool segher at chello.nl
Sat Jan 2 04:14:54 CET 1904

Klaus Seegebarth wrote:
> Segher Boessenkool wrote:
> >
> > > >[snip...snip]
> > 1% speedup is a nice optimization, and 2% slowdown is a serious performance
> > regression.
> >
> > 22% slowdown is just awful...
> Hello Segher,
> no flame war please, i appreciate Your work :-)

i'm not flaming, i'm just stating facts ;)

> If you add "IMHO" to your statements, i will accept :-)
> I only wanted to point out, that i have different needs than You.

that's fine, of course.  and yes, there's more to good code than just

> My fastest and my slowest CPU differ by a factor of 1000 (100 000 % !)
> in speed. Why should _i_ waste my time to look for 22% ?

with the current state of paflof, it's easy to get it to speed up
at least 4x or so.  i'm not concerned with optimizing it just yet,
because "premature optimization is the root of all evil", as
everyone knows.  i'm just wondering why upgrading compiler version
causes a 22% slowdown, which is awful.  i'm esp. interested in this
because the cause for the slowdown is no doubt tightly related to
the threading model paflof uses, and there is no such thing as
premature design.  i need to make sure that gcc can do a good job
on paflof's indirect threaded interpreter.

> As all my computers live inside a machine in a production
> environment, the 3 most important items for me are reliability,
> reliability and reliability. A major influence on reliability
> is the amount of energy consumed, so what i am really interested in
> is a gcc-switch, which optimizes to minimum energy per task.
> A faster completion of a task only leads to longer idle periods :-)

well, during bootup a computer draws more power than during normal
operation, so to minimize power consumption, the bootup phase has to
be as short as possible; so paflof has to be as fast as possible q.e.d.

(hehe.  just kidding.  speed is not all that important for this, but
we don't want to have it run much slower for no good reason).


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