Re: 2.5.20 RAID5 compile error

Horst von Brand
2002-06-04T18:22:55Z

Martin Dalecki <dalecki@evision-ventures.com> said:
> Well it's kind like the answer to the question: why don't do it all in hand
> optimized assembler? Or in other words - let's give the GCC guys good
> reasons for more hard work. But more seriously:
>
> Things like unlikely() tricks and other friends seldomly really
> pay off if applied randomly. But they can:
>
> 1. Have quite contrary effects to what one would expect due to
> the fact that one is targetting a single instruction set but in
> reality multiple very different CPU archs or even multiple archs.
>
> 2. Changes/improvements to the compiler.
>
> My personal rule of thumb is - don't do something like the
> above unless you did:
>
> 1. Some real global profiling.
> 2. Some real CPU cycle counting on the micro level.
> 3. You really have too. (This should be number 1!)

Anybody trying to tune code should read (and learn by heart):

@Book{bentley82:_writing_eff_progr,
author = {Jon Louis Bentley},
title = {Writing Efficient Programs},
publisher = {Prentice Hall},
year = 1982
}

(sadly out of print AFAIK)
--
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