Re: [patch] spinlocks: remove 'volatile'

[J.A. MagallÃn]

On Fri, 7 Jul 2006 17:22:22 -0500 (CDT), Chase Venters <chase.venters@xxxxxxxxxxxx> wrote:

> > .L7:
> >    movl    $1, mtx    <=========
> >    movl    spinvar, %eax
> >    movl    $0, mtx    <=========
> >    testl   %eax, %eax
> >    jne .L7
> >    popl    %ebp
> >    ret
> 
> NO! It's not better. You're still not syncing or locking the bus! If you 
> refer to the fact that the "movl $1" has magically appeared, that's 
> because you've just PAPERED OVER THE PROBLEM WITH "volatile", which is 
> _exactly_ what Linus is telling you NOT TO DO.
> 

BTW, I really don't mind if a given architecnture has to lock the bus or
say a prayer to Budha to reload a variable. I want it to be reloaded at
every (or a certain, in case of a (volatile)mtx cast) usage. The compiler
is the responsible of knowing what to do. What if nextgen P4 Xeon do not
need a bus lock ? Will you rewrite the kernel ?

--
J.A. Magallon <jamagallon()ono!com>     \               Software is like sex:
                                         \         It's better when it's free
Mandriva Linux release 2007.0 (Cooker) for i586
Linux 2.6.17-jam01 (gcc 4.1.1 20060518 (prerelease)) #2 SMP PREEMPT Wed
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