Re: spin_lock forgets to clobber memory and other smp fixes [was Re: [patch] waitqueue optimization, 2.4.0-test7]

[Jamie Lokier]

Andrea Arcangeli wrote:
> >int *p;
> >int func()
> >{
> >  int x;
> >  x = *p;
> >  __asm__ __volatile__ ("" : : : "memory");
> >  x = *p;
> >  return x;
> >}
> 
> Defintely none difference here (-fstrict-aliasing doesn't change anything
> either).
> 
> andrea@inspiron:~ > gcc -v
> Reading specs from /usr/lib/gcc-lib/i486-suse-linux/2.95.2/specs
> gcc version 2.95.2 19991024 (release)

I tried it with two compilers, one older than yours and one newer:

        .ident  "GCC: (GNU) egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)"
        .ident  "GCC: (GNU) 2.96 20000724 (experimental)"

The command lines were:

   gcc -S -O2 test4.c
   kgcc -S -O2 test4.c

In both cases, the memory read occurs before "zzz".

-- Jamie
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