Re: AA's 00_backout_gcc_3-0-patch-1

["J.A. Magallon" <jamagallon@able.es>]

On 05.27, Andrea Arcangeli wrote:
> On Mon, May 26, 2003 at 07:30:44PM -0300, Marcelo Tosatti wrote:
[...]
> 
> Overall in kernel we disagreed to follow the MUST requrested by the gcc
> developers, we often want to do comparisons of variables out of locks to
> know if we need to take the lock and work on a garbage collection or
> stuff like that and we for sure don't want to mark those variables
> volatile since they must be cached and not spilled all the time, under
> the locks. Linus as well was against using volatile for every piece of
> memory that can change under gcc. The decision is been basically to
> outsmart gcc in choosing if gcc has rights to generate kernel crashing
> code or not. This makes kernel developement even more difficult since
> you've to imagine whatever smart thing gcc can do with your not
> serialized code to know if you're forced to mark the stuff volatile, but
> it'll generate the very best performance.
> 

So you are telling that you are allowed to do something like:

int* a = 0x320;

for (i=1000 samples)
	v[i] = *a;

in kernel code and you trust gcc to not optimize the loop away ??
What is volatile is volatile...

-- 
J.A. Magallon <jamagallon@able.es>      \                 Software is like sex:
werewolf.able.es                         \           It's better when it's free
Mandrake Linux release 9.2 (Cooker) for i586
Linux 2.4.21-rc3-jam1 (gcc 3.2.3 (Mandrake Linux 9.2 3.2.3-1mdk))