Re: Optimization of conditional access to globals: thread-unsafe?

[Michael Matz <matz at suse dot de>]

Hi,

On Fri, 26 Oct 2007, David Miller wrote:

> Also, it bears repeating that whatever performance argument you make for 
> or against this issue matters little if it breaks lots of existing and 
> working code.

It matters insofar as that existing and working code is broken in a strict 
sense.  As long as that holds there's a high chance of "breaking" it at 
random times again in the future, even when the one transformation is 
changed to not "break" it anymore.  So, we either can change the 
transformation and wait for the next uproar in a couple of months or 
somehow hope that code is fixed.  But that's all the same argumentation 
like in the signed integer overflow discussion, so my hopes for the latter 
are quite low.  I mean who am I to demand that people write correct code, 
I must be insane.

> It is also important to remind people that paper standards count less 
> than common sense and what effects users on a practical level, even when 
> those paper standards allow your favorite optimization or 
> transformation.

<tongue-in-cheek>
You mean like POSIX doesn't count very much for the kernel behaviour?
</tongue-in-cheek>

You ask us to somehow regard common sense (whatever that is) and 
practicality reasons (for which set of people?) higher than paper 
standards.  How comes then, that under linux directories are still 
seekable?  Certainly when I sometimes try to convince our kernel people of 
some clever idea, they happily use the POSIX hammer quite fine.  I sigh 
and move on.  So what exactly brings you into a position to define common 
sense or which paper standards we should ignore?


Ciao,
Michael.