Re: Speeding up XCode?
Re: Speeding up XCode?
- Subject: Re: Speeding up XCode?
- From: Robert Dell <email@hidden>
- Date: Fri, 21 Oct 2005 06:19:34 -0400
George Warner wrote:
On Tue, 18 Oct 2005 22:26:41 -0400, Robert Dell <email@hidden> wrote:
If you want to understand a computer, build one from scratch. I don't mean
to buy the components at a computer fair and then a box with power supply
and then slap them together and call it "i built it myself". build
computers the way i've built them. buy the components from an IC
manufacturer, hard code the machine code, program the chips, design the
board and have a board maker make the board (my skills aren't good enough to
etch complex board patterns), solder in the parts and then test/run the
computer you've made.
The scariest part of all this is that your last name is Dell! ;-)
do I make fun of your name? I may poke fun at people's programming techniques but never some person's name, that's too personal and you don't know me that well. if you DID know me, you'd find much more things about me than my name to poke fun at.
this leads you to understand the integrated components as well as the
processor(s) you've decided to use. The PPC G4 processor implements up to 7
instructions per CPU clock cycle but under my example, i've trimmed it down
to only 1 per cycle. With the greater bandwidth the larger processors are
starting to obtain, the more instructions per cycle the processors are going
to be capable of implementing.
If you really care about this level of detail about the Power PC processors
I recommend reading the "PowerPC Performance Primer" @:
<http://developer.apple.com/technotes/tn/tn2087.html>
[\plug]
(no, I don't get paid a commission on hits. ;-)
you may also note that I've added a condition to it (if the compiler is
working properly). The speed of any program compiled by any compiler is
limited by the accuracy of it's compiler. I'd prefer to compile my code
based on if it's going to be burned into an IC for firmware so it'll take
the least amount of space and maximum amount of speed. function headers
take up a lot of space but sometimes are necessary.
I only have one question here: What does SHARK say? ;-)
If your program isn't spending more than 10% of its time running this
routine then if the absolutely best optimizer making it even a thousand
times faster isn't going to be increasing the speed of your program by more
than 10%. Is the time spent on optimizing your code worth this little of a
performance boost?
"Premature optimization is the root of all evil" - Donald Knuth.
So lets say that your routine is the #1 performance hog and that it's
responsible for more than 10% of your users "wait time". My next question
is... What does SHARK say?
The function calling overhead is usually negligible compared to processor
stalls caused by int <-> float conversions, division, cache misses, etc. I'd
worry a LOT more about those things before I'd even start to think about
function overhead.
Oh, and if you _REALLY_ care about how many cycles each instructions are
I'll refer you back to my previous two (1? ;-) questions...
What does SHARK say? ;-)
Shark says it can't find anything to monitor at all.
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